feat(mcp): add humanReadableDescription to MCP tools (#11016)

* feat(mcp): add humanReadableDescription to MCP tools

### Description
Add `humanReadableDescription` to all MCP tools to provide concise 1-sentence summaries for human consumption, and use this field in `--generate-tool-list` output and documentation tables rather than the longer AI-oriented `description`.

### Scenarios Tested
- Unit tests verify `humanReadableDescription` is attached to `ServerTool['mcp']`.
- Unit tests verify `markdownDocsOfTools()` formats the table with `humanReadableDescription` and falls back to `description` when not present.
- Ran fast test suite (`npm run mocha:fast`) and lint check (`npm run lint:changed-files`).

### Sample Commands
```bash
firebase mcp --generate-tool-list
```

* Update src/mcp/tools/index.ts

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>