fix(release): ship prebuilt assets and bump fallback version

Two release-blocking bugs traced to the same root cause: the unanchored
`data/` rule in .gitignore matched server/src/ledgrab/data/, which is
where shipped package assets live (prebuilt sounds, game adapters).
The files were never `git add`-able without -f, so they never reached
the v0.4.2 tag and CI builds couldn't include them.

- .gitignore: anchor /data/ and /server/data/ so nested package data
  dirs are not ignored.
- Track previously-excluded shipped assets:
  - server/src/ledgrab/data/prebuilt_sounds/{alert,bell,chime,ping,pop}.wav
  - server/src/ledgrab/data/game_adapters/{minecraft,rocket_league,valorant}.yaml
- Bump _FALLBACK_VERSION 0.3.0 -> 0.4.2 to match pyproject.toml.
  The Windows installer strips ledgrab-*.dist-info, so
  importlib.metadata falls back to this literal — which is why
  v0.4.2 reports v0.3.0 in the WebUI.
- Patch _FALLBACK_VERSION at bundle time in build-common.sh and
  build-dist.ps1 so future drift is auto-corrected by the build.

.gitignore

@@ -62,8 +62,12 @@ htmlcov/
 logs/
 *.log.*
 
-# Runtime data
-data/
+# Runtime data — anchor to repo root so nested package data dirs
+# (server/src/ledgrab/data/prebuilt_sounds, game_adapters) are NOT ignored.
+# An unanchored `data/` rule silently broke the v0.4.2 release by keeping
+# shipped sound assets out of the CI tag checkout.
+/data/
+/server/data/
 *.db
 *.sqlite
 *.json.bak