Runtime: bind host safety services behind RuntimeHost

[oratis]

Summary

• add a core RuntimeHost boundary that owns provider, tools, permissions, hooks, sandbox, auto-mode, and plugin directories
• keep per-turn inputs separate and expose only an explicit mode override
• migrate CLI REPL, headless, LSP, and both VS Code entry points
• retain the desktop renderer loop as an explicit packaging-ADR migration seam
• fix headless SIGINT/SIGTERM cancellation by finally passing its existing AbortSignal to the runtime

Validation

• pnpm docs:check
• pnpm lint (3 pre-existing warnings, 0 errors)
• pnpm format:check
• pnpm typecheck
• pnpm test
• pnpm build
• cargo check --manifest-path apps/desktop/src-tauri/Cargo.toml
• cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml (31 passed)

Stack

Depends on #183, #182, #181, and #180. This completes the first shared-host assembly slice; desktop moves only after the packaging ADR proves its runtime boundary.