feat(updater): in-app update on desktop, releases link on Android

Anyone who installed an AppImage or ran the Windows installer was frozen
on that version forever. Nothing in the app ever mentioned a new release
existed, and the release notes were the only announcement.

Desktop now checks a signed manifest, shows the version and its notes in
Settings, and installs and relaunches on request. The signature check is
the whole point: it is what stops a substituted download from being
installed by the app itself. Windows binaries stay unsigned for
SmartScreen purposes -- that is a code-signing certificate, a separate
problem -- but the update payload is verified against our own key.

Android is deliberately not wired to the updater. An app may not replace
its own APK; that is the package installer's job, and the plugin has no
Android implementation. It gets a link to the releases page instead of a
button that would throw.

The plugins are gated with a target-triple cfg rather than
cfg(desktop). Cargo only evaluates target cfgs in a [target.'cfg(..)']
table, so cfg(desktop) matches nothing, silently drops the dependency,
and fails much later with "Permission updater:default not found" -- which
is exactly what the first attempt here did.

Where the manifest lives took some finding. This Gitea serves
/releases/download/<tag>/<asset> but 404s on
/releases/latest/download/<asset> (verified against a real asset), so
there is no stable latest-release URL. The gitea-pages branch is
force-pushed wholesale by publish-docs.yml, so it cannot host the file
either. latest.json therefore gets its own orphan branch, read over the
raw-file URL, and is published from a scratch repo in RUNNER_TEMP rather
than by switching branches in the checkout -- doing that would have left
the following steps standing on a one-commit history, and the next step
but one runs release:notes against the real commit range.

Also fixed, all of it release-integrity:

  - "appimage" is in bundle.targets. The release notes have advertised an
    AppImage for months; tauri.conf.json never built one, the artifact
    step globbed for *.AppImage, found nothing, and said nothing. The
    step now fails instead.
  - The .AppImage.tar.gz/.sig pair and the NSIS .sig are collected. A
    manifest referencing a signature that was never uploaded fails only
    on the user's machine, so the manifest step also refuses to write an
    entry with an empty signature.
  - Release notes are generated by release:notes from the traceability
    graph, which is what CLAUDE.md has asked for all along, instead of a
    fixed heredoc that said "see CHANGELOG.md for detailed changes" and
    linked "GitHub Issues" on a Gitea-hosted project.
  - The notes tell users how to verify a download with SHA256SUMS.

Requirements UR-077 / DR-217, tests UT-208 (12 cases over the version
comparison and the platform decision, including that a pre-release does
not offer itself as an upgrade to the matching release).

Verified: 1070 frontend tests, cargo check for both the host and
aarch64-linux-android (confirming the plugins are absent there), clippy
-D warnings, svelte-check 0 errors.

src-tauri/Cargo.lock

@@ -150,6 +150,15 @@ version = "1.0.100"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a23eb6b1614318a8071c9b2521f36b424b2c83db5eb3a0fead4a6c0809af6e61"
 
+[[package]]
+name = "arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d036a3c4ab069c7b410a2ce876bd74808d2d0888a82667669f8e783a898bf1"
+dependencies = [
+ "derive_arbitrary",
+]
+
 [[package]]
 name = "ascii"
 version = "1.1.0"
@@ -789,6 +798,17 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "derive_arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e567bd82dcff979e4b03460c307b3cdc9e96fde3d73bed1496d2bc75d9dd62a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.112",
+]
+
 [[package]]
 name = "derive_more"
 version = "0.99.20"
@@ -1095,6 +1115,16 @@ dependencies = [
  "rustc_version",
 ]
 
+[[package]]
+name = "filetime"
+version = "0.2.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c287a33c7f0a620c38e641e7f60827713987b3c0f26e8ddc9462cc69cf75759"
+dependencies = [
+ "cfg-if",
+ "libc",
+]
+
 [[package]]
 name = "find-msvc-tools"
 version = "0.1.6"
@@ -2046,6 +2076,8 @@ dependencies = [
  "tauri-build",
  "tauri-plugin-opener",
  "tauri-plugin-os",
+ "tauri-plugin-process",
+ "tauri-plugin-updater",
  "tauri-specta",
  "tempfile",
  "tiny_http",
@@ -2338,6 +2370,12 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6877bb514081ee2a7ff5ef9de3281f14a4dd4bceac4c09388074a6b5df8a139a"
 
+[[package]]
+name = "minisign-verify"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22f9645cb765ea72b8111f36c522475d2daa0d22c957a9826437e97534bc4e9e"
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"
@@ -2643,6 +2681,18 @@ dependencies = [
  "objc2-core-foundation",
 ]
 
+[[package]]
+name = "objc2-osa-kit"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f112d1746737b0da274ef79a23aac283376f335f4095a083a267a082f21db0c0"
+dependencies = [
+ "bitflags 2.10.0",
+ "objc2",
+ "objc2-app-kit",
+ "objc2-foundation",
+]
+
 [[package]]
 name = "objc2-quartz-core"
 version = "0.3.2"
@@ -2775,6 +2825,20 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "osakit"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "732c71caeaa72c065bb69d7ea08717bd3f4863a4f451402fc9513e29dbd5261b"
+dependencies = [
+ "objc2",
+ "objc2-foundation",
+ "objc2-osa-kit",
+ "serde",
+ "serde_json",
+ "thiserror 2.0.17",
+]
+
 [[package]]
 name = "pango"
 version = "0.18.3"
@@ -4193,6 +4257,17 @@ dependencies = [
  "syn 2.0.112",
 ]
 
+[[package]]
+name = "tar"
+version = "0.4.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f6221d9a6003c78398e3b239969f352578258df48c8eb051caadae0015bc840"
+dependencies = [
+ "filetime",
+ "libc",
+ "xattr",
+]
+
 [[package]]
 name = "target-lexicon"
 version = "0.12.16"
@@ -4372,6 +4447,48 @@ dependencies = [
  "thiserror 2.0.17",
 ]
 
+[[package]]
+name = "tauri-plugin-process"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d55511a7bf6cd70c8767b02c97bf8134fa434daf3926cfc1be0a0f94132d165a"
+dependencies = [
+ "tauri",
+ "tauri-plugin",
+]
+
+[[package]]
+name = "tauri-plugin-updater"
+version = "2.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "27cbc31740f4d507712550694749572ec0e43bdd66992db7599b89fbfd6b167b"
+dependencies = [
+ "base64 0.22.1",
+ "dirs",
+ "flate2",
+ "futures-util",
+ "http",
+ "infer",
+ "log",
+ "minisign-verify",
+ "osakit",
+ "percent-encoding",
+ "reqwest",
+ "semver",
+ "serde",
+ "serde_json",
+ "tar",
+ "tauri",
+ "tauri-plugin",
+ "tempfile",
+ "thiserror 2.0.17",
+ "time",
+ "tokio",
+ "url",
+ "windows-sys 0.60.2",
+ "zip",
+]
+
 [[package]]
 name = "tauri-runtime"
 version = "2.9.2"
@@ -5877,6 +5994,16 @@ dependencies = [
  "pkg-config",
 ]
 
+[[package]]
+name = "xattr"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32e45ad4206f6d2479085147f02bc2ef834ac85886624a23575ae137c8aa8156"
+dependencies = [
+ "libc",
+ "rustix",
+]
+
 [[package]]
 name = "yoke"
 version = "0.8.1"
@@ -6041,6 +6168,18 @@ dependencies = [
  "syn 2.0.112",
 ]
 
+[[package]]
+name = "zip"
+version = "4.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "caa8cd6af31c3b31c6631b8f483848b91589021b28fffe50adada48d4f4d2ed1"
+dependencies = [
+ "arbitrary",
+ "crc32fast",
+ "indexmap 2.12.1",
+ "memchr",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.8"