fix: stop committing generated frontend build output (wwwroot rehash noise)

Root cause (CURRENT_ROADMAP.md item #3): wwwroot/assets/* and
wwwroot/index.html under KArtSell.Host are 100% Vite build output (no
hand-authored files in there) but were committed to git. Every local
dotnet build re-triggers pnpm build via the BuildFrontend MSBuild
target, which produces new content-hashed filenames even when no
frontend source changed, and the old hashed files were never cleaned
up (4 of the 6 committed asset files were already orphaned/unreferenced
before this fix, confirmed by diffing wwwroot/index.html's script/link
tags against what was actually on disk).

Investigated whether the committed output was load-bearing for
deployment before picking a fix:
- .gitea/workflows/deploy.yml (the real production deploy path) already
  wipes wwwroot and rebuilds it fresh from pnpm build on every deploy,
  so the committed files were never actually used there.
- .gitea/workflows/ci.yml's `publish` job (Gitea Release zip) was the
  only place actually depending on the committed wwwroot contents,
  since it runs `dotnet publish` without ever building the frontend.

Given that, committing the hashed output was pure architectural
mistake with no deployment benefit, and the smaller/more correct fix
is to stop tracking it rather than bolt MSBuild Inputs/Outputs
incrementality onto the BuildFrontend target (which would also be
fragile: git checkouts/worktrees can normalize file mtimes in ways
that defeat timestamp-based up-to-date checks).

Fix:
- .gitignore: ignore src/KArtSell.Host/wwwroot/assets/ and
  wwwroot/index.html (generated by BuildFrontend target locally and by
  deploy.yml in production).
- git rm --cached the 7 previously-tracked generated files.
- ci.yml publish job: add the same pnpm install/build + wipe-and-copy
  step deploy.yml already uses, so the release zip still ships a real
  frontend build instead of losing it now that git no longer carries it.
- Left the BuildFrontend MSBuild target itself unchanged (still runs
  pnpm build on every local `dotnet build`) since re-running it is no
  longer a problem now that its output isn't tracked.

Verified (not just asserted):
- `dotnet build KArtSell.sln -c Release` run twice in a row: `git
  status`/`git diff --stat` identical after both runs (only the 9
  intentional lines in .gitignore/ci.yml), even though wwwroot/assets
  on disk got fresh hashed filenames both times.
- Reverted to pre-fix state and ran a single `dotnet build` with zero
  source changes: reproduced the bug exactly as described -
  wwwroot/index.html showed a 13-line diff and 2 new untracked hash
  files appeared, with the old stale ones left behind. Then restored
  the fix and re-verified the two-consecutive-build check above.
- `cd frontend && pnpm install --frozen-lockfile && pnpm typecheck &&
  pnpm build` all pass cleanly on their own.
- `dotnet test tests/KArtSell.ModelOperations.UnitTests` still 54/54
  passing after the build changes.

Separate, out-of-scope finding recorded in CURRENT_ROADMAP.md: ~130
frontend/src/**/*.js files compiled from .ts/.vue siblings (plus
tsconfig.tsbuildinfo, vite.config.js) are also committed and also
regenerate on every `pnpm build` via `vue-tsc -b`, because
tsconfig.json has no `noEmit: true`. Same class of problem, not fixed
here to keep this PR to one goal.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -100,6 +100,25 @@ jobs:
       - uses: actions/setup-dotnet@v4
         with:
           dotnet-version: '10.0.x'
+      - uses: pnpm/action-setup@v4
+        with:
+          version: 10
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+          cache-dependency-path: frontend/pnpm-lock.yaml
+
+      - name: Build frontend into Host static assets
+        # wwwroot/assets and wwwroot/index.html are gitignored build output (see
+        # CURRENT_ROADMAP.md item #3) -- this release zip must build them fresh,
+        # the same way .gitea/workflows/deploy.yml does for production.
+        run: |
+          pnpm install --frozen-lockfile
+          pnpm build
+          find ../src/KArtSell.Host/wwwroot -mindepth 1 -delete
+          cp -R dist/. ../src/KArtSell.Host/wwwroot/
+        working-directory: frontend
 
       - name: Publish Release Build
         run: |