Port /impeccable generate to the engine crates

The Node-era server, CLI, hook, and pin halves of the generate command move
into the Rust workspace, with the protocol unchanged:

- crates/live: POST /agent-target is held open on a channel plus a timer
  thread (the manual-apply deferred pattern), releasing its turnstile
  ticket before it parks like /poll; /agent-target-result resolves it;
  /agent-target-claim is the roll call with its renewable lease. SSE
  connections carry the overlay's clientId: a late overlay is replayed
  every pending target, and a disconnect retires that overlay's report,
  releases its lease, and re-judges each roll call. Shutdown drains held
  requests with server_stopping.
- crates/live/src/live_generate.rs: the live-generate verb (the router
  already forwards every live* verb), same flags, verdicts, and
  _instructions, spelled with the engine's self command.
- crates/hook: every entry stands down on live preview markers
  (skipped: live-preview), checking the proposed content and the file on
  disk for hook-before-edit.
- crates/context: pin accepts generate; the crate's command-metadata.json
  copy carries its entry.

Tests: crates/cli/tests/agent_target.rs (six HTTP cases with an SSE reader),
tests/live-agent-target.test.mjs rewritten to drive the binary (28 cases,
registered in the live suite), hook stand-down cases, oracle goldens for
live-generate plus the re-recorded pin list goldens, the e2e prompt
assertion waiting for the journaled event, and the contract documented in
docs/CLI-CONTRACT.md.

AI-assisted: implemented and tested with Claude Code under maintainer
direction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/test-suites.mjs

@@ -140,12 +140,14 @@ export const SUITES = {
       /^skill\/(reference\/live\.md|scripts\/live-browser)/,
       /^tests\/live-e2e\//,
       /^tests\/lib\/engine-bin\.mjs$/,
+      /^tests\/live-agent-target\.test\.mjs$/,
     ],
     commands: [
       {
         runner: 'node',
         files: [
           'tests/live-reference.test.mjs',
+          'tests/live-agent-target.test.mjs',
           'tests/live-browser-ignores.test.mjs',
           'tests/live-browser-source.test.mjs',
           'tests/live-e2e-agent-output.test.mjs',