docs: fold shipped specs into the architecture docs and delete them

A spec was a promise; sixteen of them had become descriptions of code that
already shipped, sitting beside four that describe work still outstanding, with
nothing in the file telling the two apart. Half the statuses were also wrong —
audio-equalizer read "Accepted" with the EQ live on both platforms, the native
video spec said the flag stays off after the default was flipped on.

The shipped designs move into docs/architecture, which is the maintained
description of the build, and the spec files go. Git history keeps the
originals; what a future change still needs is carried across:

- 01-rust-backend: favourites rewritten (the old section named a file that no
  longer exists and called shipped buttons "planned"), domain vocabulary owned
  by Rust (SearchScope, exclusions, the bitrate ladder), background workers
- 02-svelte-frontend: app shell and chrome, library mosaic, series/episode
  navigation, downloaded browse, safe-area insets, native-video store, logging
- 03-data-flow: locally-indexed search
- 05-platform-backends: audio settings on ExoPlayer, the equalizer's band
  vocabulary, native video compositing, the background-audio handoff
- 06-downloads-and-offline: one storage model, offline catalog visibility
- 09-security: path confinement and input binding

docs/specs/README.md now says what the directory is for and where each shipped
design went. Deferred work the specs recorded is kept beside the code it
concerns rather than lost: season-bounded autoplay, the two dead search
commands, why indexing is a full crawl.

requirements.md had fourteen stale statuses — Android audio parity still read
"Linux only", DR-150 still said the native-video default was off, DR-190 was
Proposed after DR-196 implemented it, and five tooling requirements were
Proposed after landing. Three unbuilt specs suggested requirement ids that have
since been allocated to other work; each now carries a warning.

scripts/README.md

@@ -112,7 +112,8 @@ typos and renames that missed a call site went unreported for months.
 > unscoped (hanging on ~40 GB of `target/` artifacts), and in one case reported
 > "all requirements implemented" from an empty result set. `extract-traces.ts` is
 > the single source of truth for requirement coverage. See
-> [docs/specs/req-coverage-script-removal.md](../docs/specs/req-coverage-script-removal.md).
+> it reported `Total Requirements: 1` and then "All requirements have
+> implementations!". Nothing referenced it. Use `bun run traces:coverage`.
 
 Example TRACES comment in code:
 ```typescript

scripts/check-frontend-boundary.sh

@@ -33,7 +33,8 @@
 # This check was hardened in July 2026 after the audit found it passing on the
 # very leak it was written for: the original pattern was anchored to
 # `includeItemTypes:` at the query site, so assigning the same array to a named
-# const evaded it entirely. See docs/specs/boundary-tripwire-hardening.md (DR-094).
+# const evaded it entirely (DR-094). The pattern below is the hardened one: it
+# matches an item-type array literal anywhere, not just at a query site.
 #
 # Escaping a genuine exception: add the file+reason to the ALLOWLIST below.
 
@@ -59,7 +60,7 @@ ALLOWLIST=(
   # BORDERLINE — leans domain: the container set grows when Jellyfin adds a
   # container type. TODO: replace with a backend-supplied `MediaItem.isContainer`
   # flag and remove this entry. Tracked in
-  # docs/specs/boundary-tripwire-hardening.md §Out of scope.
+  # a backend-supplied flag; deferred rather than bundled with the tripwire work.
   "src/lib/components/downloads/DownloadedBrowse.svelte"
 )
 

scripts/extract-traces.ts

@@ -229,7 +229,7 @@ function extractTraces(): TracesData {
 // CI gate previously divided by frozen literals (UR/39, IR/24, DR/48, JA/3,
 // total 114) while the real file had grown to 211 requirements, so it reported
 // 158% coverage and the 50% threshold became unreachable — the gate could not
-// fail. See docs/specs/traceability-gate-repair.md.
+// fail. See docs/traceability-ci.md, "Coverage Thresholds".
 //
 // TRACES: | DR-093
 // ---------------------------------------------------------------------------