feat: add Personal Cursor Cloud multi-share setup

[Kashkovsky]

Summary

• promote the legacy Cursor Cloud Git profile to stable Personal Cursor Cloud while retaining old MCP toolset aliases
• expose up to 16 explicit Git memory shares through one bounded personal MCP with per-share sync throttling and explicit write routing
• install a Cloud-safe Cursor rule plus three Cursor 4.6 Agent Skills during environment bootstrap
• add a standalone Personal Cursor Cloud website guide covering environment creation, one-MCP registration, multiple shares, verification, and troubleshooting

Validation

• pre-commit: full lint, Prettier write/check, TypeScript and website typecheck
• bun --bun vitest run test/integration/cursor-cloud.test.ts test/unit/mcp.test.ts
• bun --bun vitest run test/integration/share.sync.test.ts test/unit/effect-share.test.ts
• focused Cursor Cloud, agent-instruction, onboarding, MCP, and website unit tests
• bun run check:self-contained
• bun run site:build (51 crawler-visible documentation pages)
• exact-HEAD global install and installed CLI/MCP smoke with two local Git shares and generated Cursor skills

Review

Requested dev-cycle completed in three iterations with zero critical or important findings. The final incremental pass also verified the file-length extraction and both legacy MCP aliases.