docs+ci: harden the docs-first rule + add a non-blocking parity-doc reminder

CLAUDE.md Conventions: turn "read docs before exploring" into a hard rule with red-flag
framing (do NOT reverse-engineer conventions from source; applies to subagents too) and a
"which doc to update in the same PR" table. Add a lightweight, PR-only, NON-BLOCKING
`docs-reminder` CI job that warns when a screen/route change skips
docs/blazor-route-parity.md. No dotnet/node in that job (no actions/cache), so it can't hit
the VM-127 cache-save issues (server-management#570). Documented in docs/ci-cd.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/docker-build.yml

@@ -298,3 +298,36 @@ jobs:
             echo "===== container logs (tail) ====="; docker logs "$NAME" 2>&1 | tail -n 40 || true
             exit 1
           fi
+
+  # Non-blocking nudge: if a PR migrates/adds a route but forgets the parity tracker, warn.
+  # The rule lives in CLAUDE.md → Conventions; this only surfaces an easy-to-miss omission.
+  # Deliberately no setup-dotnet/setup-node (and thus no actions/cache) so it can't hit the
+  # cache-save issues seen on the relocated runner (server-management#570).
+  docs-reminder:
+    name: Docs update reminder
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Warn when a screen/route change skips the parity doc
+        run: |
+          base_ref="${{ github.base_ref }}"
+          git fetch --no-tags --depth=100 origin "$base_ref" || true
+          changed="$(git diff --name-only "origin/${base_ref}...HEAD" 2>/dev/null || true)"
+          echo "Changed files in this PR:"; printf '%s\n' "$changed"
+          screen_or_route=no
+          if printf '%s\n' "$changed" | grep -Eq '^web/src/screens/.+\.tsx$|^ErsatzTV/LegacyUiRedirects\.cs$'; then
+            screen_or_route=yes
+          fi
+          parity=no
+          if printf '%s\n' "$changed" | grep -qx 'docs/blazor-route-parity.md'; then
+            parity=yes
+          fi
+          if [ "$screen_or_route" = yes ] && [ "$parity" = no ]; then
+            echo "::warning::This PR touches a SPA screen or LegacyUiRedirects.cs but does not update docs/blazor-route-parity.md. If you added/migrated/redirected a route, update the parity tracker (and docs/domain-model.md) in THIS PR — see CLAUDE.md → Conventions."
+          else
+            echo "Parity-doc reminder: nothing to flag."
+          fi