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.

这项工作涉及三项不同的配置更改。首先，找到 TypeScript 配置文件（例如 `renderers/lit/tsconfig.json`），添加 `"noImplicitOverride": true`。其次，找到 ESLint 配置（`eslint.preset.mjs`），为内部包的导入添加 `no-restricted-imports` 规则。第三，检查现有的 `tsconfig.json` 文件，确保已设置 `strict: true`，或者添加相关的 ESLint 规则。检查 CI 流水线配置，确保这些检查会运行。“完成”意味着在代码库中强制执行这些新规则后，CI 通过。

由索引模型根据 Issue 内容生成。