docs: align site with MCP 2026 boundaries

[dajiaohuang]

Summary

• replace the public authoritative contract v1 and connection-scoped catalog story with the MCP 2026-07-28 modern target and application contract v2
• document deterministic authorization-scoped catalogs, Host task projections, explicit owner/TTL handles, per-request delegated identity, and the token-passthrough prohibition
• align Local and Hosted transport semantics, immutable component locks, canary upgrades, and whole-lock rollback without archived repository fallbacks
• add deterministic content checks that reject the former public contract claims and require the modern boundary documentation

Historical dated news remains unchanged. The Pages workflow already builds only this repository and has no archived or cross-repository release input.

Validation

• npm run check — content checks, Astro production build, and built-site checks pass for 8 bilingual routes
• npm run check:external — 17 external links pass with no access-limited warnings
• git diff --check