Runtime safety: mandatory policy and real cancellation

[oratis]

Summary

• make the central tool dispatcher impossible to omit and fail safe for legacy callers
• give LSP, VS Code, and desktop explicit safe policies
• propagate aborts through providers, pending approvals, Node process groups, and Tauri/Rust process groups
• preserve worktree branches and reject removal when user changes are present

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 (29 passed)

Stack

Depends on #180. This is the safety/cancellation slice of PR 1 in docs/CODEX_ALIGNMENT_PLAN.md; RuntimeHost assembly and background ownership can follow without weakening these invariants.