[codex] Add extension tool contract catalog

[MiguelsPizza]

Summary

Adds side-effect-free, MCP-complete contract exports for the direct-action @mcp-b/extension-tools surface covering bookmarks, history, storage, tab groups, tabs, and windows.

What changed

• Added contract-only exports under @mcp-b/extension-tools/contracts plus targeted group subpaths.
• Exported stable tool names, group/action IDs, Zod input schemas, MCP JSON input schemas, output schemas for structured tools, annotations, and namespaced mcp-b/extension-tools metadata.
• Refactored the six direct-action execution classes to consume the exported contracts instead of redefining names/descriptions/schemas locally.
• Added structuredContent wrapping for successful direct-action calls whose contracts declare an output schema.
• Added contract tests for MCP tools/list shape, object-root schemas, annotations, metadata, side-effect-free import behavior, catalog maps, and runtime registration drift.
• Kept browser runtime registration from advertising outputSchema for now because extension-page clients currently compile output schemas through Ajv, which violates MV3 CSP; the contract exports still carry outputSchema for Cloudflare/Node hydration.

Validation

• pnpm --filter @mcp-b/extension-tools run check
• pnpm --filter @mcp-b/extension-tools test
• pnpm --filter @mcp-b/extension-tools run typecheck
• pnpm --filter @mcp-b/extension-tools run build
• pnpm --filter @mcp-b/extension-tools run test:e2e
• node --input-type=module -e "delete globalThis.chrome; const m = await import('./packages/extension-tools/dist/contracts/index.js'); console.log(m.EXTENSION_TOOL_CONTRACTS.length);"

Notes

This completes the contract/source-of-truth work for the current direct-action Chrome tool groups. The remaining generated Chrome API wrappers still use their existing registration style and should be migrated with the same contract pattern in follow-up slices.