Fix notification plugin loading on OpenCode 2.0.27

[eivindjonassen]

Replace the beta SDK that calls Schema.isStartsWith with the matching stable plugin SDK. OpenCode shares its bundled Effect runtime, so the old SDK failed during server import even though a standalone Node import passed.

Update server and TUI imports, remove the obsolete tui flag, and add an opt-in live-server smoke check. Verified plugin typecheck, 18 tests, build, targeted lint, and active server status after restart.

Summary

Describe the user-visible or contract-level change.

Verification

• pnpm check
• pnpm native:doctor
• Tests cover the changed behavior.
• Platform behavior is verified on the affected targets, or the gap is documented.
• No credentials, addresses, identifiers, user content, private paths, or deployment files are included.
• Documentation and TODO.md reflect the resulting behavior.