Enforce 1P-compatible coding standards via Linting and TS Config

To prevent new code from inadvertently breaking the Google 1P import process, we need to add several automated checks (formatting/linting) to our CI pipeline. This work should be completed following the merge of PR #1655.

### 1. Enforce `override` keyword (TypeScript)
We need to enable the `"noImplicitOverride": true` compiler option in our TypeScript configuration (e.g., `renderers/lit/tsconfig.json`).
* **Why**: This will force the compiler to throw an error if a developer overrides a method (such as Lit's `render()` or `updated()`) or a property (`static styles`) without explicitly providing the `override` keyword, maintaining compatibility with Google3's strict TypeScript compilation rules.

### 2. Prevent External Imports Inside Packages (ESLint)
We need to add the `no-restricted-imports` rule to our ESLint configuration (`eslint.preset.mjs` or package-specific configs).
* **Why**: To explicitly forbid importing from `@a2ui/lit/*` (or similar package names) from within that package's own source directories. This will enforce the use of relative imports (`../` or `./`) for internal file resolution, which is required for monorepo environments.

### 3. Enforce Strict Component Property Typing (TypeScript / ESLint)
We need to enhance our type strictness, either via `tsconfig.json` (`strict: true`) or specific ESLint rules like `@typescript-eslint/typedef`.
* **Why**: This ensures that properties (like input `type`s in `TextField`) are explicitly typed (e.g., `'text' | 'number' | 'password'`) rather than relying on loose string inference, preventing mismatched types downstream in Google3.

Le travail comporte trois changements de configuration distincts. Premièrement, localisez le fichier de configuration TypeScript (par exemple, `renderers/lit/tsconfig.json`) pour y ajouter `"noImplicitOverride": true`. Deuxièmement, trouvez la configuration ESLint (`eslint.preset.mjs`) pour y ajouter une règle `no-restricted-imports` pour les imports de packages internes. Troisièmement, examinez les fichiers `tsconfig.json` existants afin de vérifier que `strict: true` est défini, ou ajoutez les règles ESLint pertinentes. Vérifiez la configuration du pipeline CI pour vous assurer que ces contrôles sont exécutés. « Terminé » signifie que la CI passe avec ces nouvelles règles appliquées à la base de code.

Rédigé par le modèle d'indexation à partir du texte de l'issue.