fix(release): keep git tree clean for goreleaser

The dist copy deleted tracked .keep and overwrote tracked index.html —
dirty tree aborted the release. index.html is now untracked (bare clones
serve 404 instead of a stale stub), .keep alone satisfies go:embed, and
the workflow merges into dist/ without rm. fetch-depth: 0 for tag history.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.gitignore

@@ -5,7 +5,6 @@ packages/api-client/dist/
 packages/api-client/src/schema.d.ts
 apps/backend/internal/web/dist/*
 !apps/backend/internal/web/dist/.keep
-!apps/backend/internal/web/dist/index.html
 
 # data / runtime
 data/*