fix: update release workflow and docs for 0.5.0 single-lockfile refactor

- release.yml: replace per-variant lockfile generation loop with a
  single 'uv lock'; add idempotent release creation (skip if tag
  already has a release so re-triggered runs don't 422)
- docker-publish.yml: remove stale uv-cpu/rocm/intel.lock entries
  from paths-ignore (those files no longer exist)
- README: CACHE_DIR description now names winnow_tracker.db; tracker
  description mentions SQLite

.github/workflows/docker-publish.yml

@@ -12,9 +12,6 @@ on:
       - ".github/workflows/lint.yml"
       - ".github/dependabot.yml"
       - "uv.lock"
-      - "uv-cpu.lock"
-      - "uv-rocm.lock"
-      - "uv-intel.lock"
   workflow_call:
     inputs:
       tag: