chore: give the project its own identity instead of the scaffold's

Cargo.toml still carried `description = "A Tauri App"` and `authors = ["you"]`,
package.json's description was empty with no author or repository, and there was
no LICENSE file at all despite package.json declaring MIT.

The user-visible half matters more. productName was the scaffold's lowercase
"jellytau", which is what the Android *release* build shows under its icon and
what the deb/rpm/NSIS bundles carry as their display name. It went unnoticed
because build.gradle.kts overrides the label to "JellyTau Debug" for the debug
build type — the install a developer sees every day was the only correctly-cased
one. mainBinaryName pins the executable filename to "jellytau" so
build-windows-cross.sh and the Arch PKGBUILD, which both resolve it by name,
need no change.

strings.xml moves into the canonical android tree rather than being edited in
gen/, since sync-android-sources.sh already copies res/values/*.xml — so the fix
survives the next regeneration.

Bundle metadata (publisher, copyright, category, descriptions, licence) was
absent entirely, so the packages shipped with no maintainer or description. The
hand-written PKGBUILD and .desktop had all of it; only the generated packaging
was wrong.

Adds .env.example: three scripts require signing vars from a gitignored .env
and .gitignore already whitelists the example, but none existed.

TRACES: | DR-214

.env.example

@@ -0,0 +1,23 @@
+# Local Android release signing.
+#
+# Copy to `.env` and fill in. `.env` is gitignored and is the single source of
+# truth for local release signing — scripts/write-keystore-properties.sh reads
+# it and regenerates src-tauri/gen/android/keystore.properties before every
+# release build, because `tauri android init` overwrites that file.
+#
+# Only needed for `bun run android:build:release`. Debug builds sign with the
+# local debug keystore and need nothing here.
+#
+# CI does not use this file: build-release.yml reconstructs the keystore from
+# the ANDROID_KEYSTORE_BASE64 secret and writes the same properties itself.
+
+# Key alias inside the keystore.
+ANDROID_KEY_ALIAS=jellytau
+
+# Absolute path to the .jks. Keep it outside the repo, or in the gitignored
+# android-keystore/ directory.
+ANDROID_KEYSTORE_FILE=/absolute/path/to/jellytau-release.jks
+
+# Keystore and key passwords. These are secrets — never commit the filled-in .env.
+ANDROID_KEYSTORE_PASSWORD=
+ANDROID_KEY_PASSWORD=