feat(primer): broaden Codex alignment hold to all real consumers; pre+post slot window

Address review gaps in the primer-alignment hold so the fixed-slot primer
reliably wins the first-request race for the shared Codex window:

- Extract the time-based hold into a dependency-free leaf module
  (codex-primer-alignment.ts) so every Codex path can share it without import
  cycles.
- Add a pre-slot hold window (2 min) in addition to the post-slot (5 min) and
  the 04-08 KST dawn gap, closing the "request a beat before the slot" gap.
- Hold the dashboard's periodic Codex warm-up too: runCodexWarmupCycle now
  skips during the hold unless called with isPrimer (the scheduled primer sets
  it), so the warm-up can't anchor the window ahead of the primer.
- Remove the urgent @-mention bypass on the reviewer/arbiter and owner holds —
  the reset is anchored unconditionally as requested.
- Reviewer/arbiter hold resumes exactly once after the window via the existing
  per-revision claim (poll re-detect; no double run).

Note: the unified lease boundary (syncHostCodexSessionFiles) is synchronous and
throws a terminal "Codex unavailable", so it can't host a clean defer+resume;
gating stays at the async turn-scheduling layer that can re-queue. Honest caveat
unchanged: making the primer first is necessary but not sufficient to pin a
trailing reset.

Verified: typecheck, build, bundle-smoke; full suite 1482 passing with only the
9 pre-existing env-config baseline failures (service-routing/paired-context/
migrate-room owner=claude vs codex-main); new alignment + warmup-hold tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/usage-primer.test.ts

@@ -71,7 +71,7 @@ describe('usage-primer', () => {
         maxUsagePct: 100,
         maxD7UsagePct: 100,
       }),
-      { ignoreZeroUsageWindow: true },
+      { ignoreZeroUsageWindow: true, isPrimer: true },
     );
   });
 });