ci: freeze the web lint warning cap at zero (batch 5)

The 99-warning legacy backlog from the React 19 / eslint-plugin-react-hooks
v6 upgrade is fully burned down — CI now fails on any new warning. The
compiler rules stay demoted to "warn" so local dev output remains readable;
the eslint config comments now point to the established fix patterns
instead of the retired ratchet.

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

.github/workflows/ci.yml

@@ -77,12 +77,11 @@ jobs:
       - name: Typecheck
         run: npx tsc --noEmit
 
-      # Errors fail outright. Warnings are ratcheted: the cap is the current
-      # count of accepted warnings (React-Compiler hooks-rule findings demoted
-      # in eslint.config.mjs + exhaustive-deps) — when you fix warnings, lower
-      # the cap to match; never raise it.
+      # Errors fail outright, and so does ANY warning: the codebase is
+      # warning-clean and must stay that way — fix new findings, never
+      # raise the cap.
       - name: Lint
-        run: npm run lint -- --max-warnings 99
+        run: npm run lint -- --max-warnings 0
 
       - name: Tests
         run: npm test