feat(web): add ESLint 10 with flat config and CI integration

- Install ESLint 10 + TypeScript-ESLint + React hooks plugins
- Create eslint.config.js with flat config format
- Fix conditional hooks violations in agents-page, task-list, knowledge-chart
- Fix unused variables and useless assignments
- Add lint step to CI workflow before build
- Remove unused eslint-disable comments

Rules configured:
- rules-of-hooks: error (critical)
- exhaustive-deps: off (intentional patterns)
- no-explicit-any: off (pragmatic casts)
- no-console: off (dev convenience)

.github/workflows/ci.yaml

@@ -73,4 +73,5 @@ jobs:
           cache: pnpm
           cache-dependency-path: ui/web/pnpm-lock.yaml
       - run: pnpm install --frozen-lockfile
+      - run: pnpm lint
       - run: pnpm build