skill(add-gmail-tool): OneCLI-native Gmail MCP tool

Adds /add-gmail-tool — a Utility skill that installs Gmail as an MCP tool
in NanoClaw v2 using OneCLI for credential injection. No raw OAuth tokens
ever reach the container; the gateway swaps the "onecli-managed" stub
bearer for the real token at request time.

Scope (3 files):
- container/Dockerfile: pnpm global-install of
  @gongrzhe/server-gmail-autoauth-mcp@1.1.11, pinned behind GMAIL_MCP_VERSION.
  Also pins zod-to-json-schema@3.22.5 to avoid an ERR_PACKAGE_PATH_NOT_EXPORTED
  crash: the MCP server's loose zod range resolves zod@3.24.x while
  zod-to-json-schema@3.25.x imports the zod/v3 subpath that only exists in
  zod>=3.25.
- container/agent-runner/src/providers/claude.ts: adds 'mcp__gmail__*' to
  TOOL_ALLOWLIST so the agent can invoke the server's tools.
- .claude/skills/add-gmail-tool/SKILL.md: pre-flight checks (OneCLI Gmail app
  connected, stubs present, mount allowlist covers ~/.gmail-mcp, agent
  secret-mode), per-group wiring in container.json (mount + mcpServers),
  verification steps, troubleshooting, removal instructions. Credits to
  gongrzhe for the MCP server and the add-atomic-chat-tool / add-vercel
  skill patterns.

Addresses #1500 (proxy Gmail OAuth through credential proxy) on the Gmail
side. Overlaps in intent with #1810 but stays surgical — no bundled
unrelated changes.

Tested end-to-end on Linux/Docker: CLI and WhatsApp self-chat agents can
list labels, search/read/send mail via OneCLI-injected tokens.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

container/agent-runner/src/providers/claude.ts

@@ -55,6 +55,7 @@ const TOOL_ALLOWLIST = [
   'Skill',
   'NotebookEdit',
   'mcp__nanoclaw__*',
+  'mcp__gmail__*',
 ];
 
 interface SDKUserMessage {