feat(graceful-handoff): sync the ritual with the global session-end mechanism (v3.2.0)

SKILL.md had drifted from the global CLAUDE.md on two counts, both verified by
grep before the rewrite: the STATE.md template predated the mandatory `board:`
line and the `route:`/`route-last:` lines, and the closing line still demanded
three fields where six are now required (Innboks, Modell neste okt,
Oppstartskommando were missing).

- New step 3 routes the next session via `repo-mailbox:route` BEFORE the Write.
  It cannot run after the commit: the emitted lines live inside STATE.md, so
  routing afterwards would dirty a file that was just committed. One invocation
  feeds both the three comment lines and the closing line's model fields.
- `repo-mailbox` stays a soft dependency — documented fallback if it is absent
  or the cross-plugin Skill invocation is blocked. `route.sh`'s path is
  deliberately not hardcoded (plugin cache, versioned, drifts).
- The single-line constraint on the three comments is now in prose: `board.sh`
  reads the first non-blank, non-heading, non-`<!--` line under the heading as
  the repo's next step, so a wrapped `rationale=` corrupts the board.
- Closing line 3 -> 6 fields. The Innboks field reports what the session did
  rather than re-querying the mailbox — inbox handling belongs first in a
  session, and "no inbox injected" must never be reported as "empty".
- STATE format consolidated to ONE copy. Repo CLAUDE.md restated it with the
  same defect; it now points at SKILL.md step 4 as the authority, following the
  model-rubric precedent (two copies drift, prose cannot be tested).
- allowed-tools gains `Skill`. `plugin.json` description left unchanged on
  purpose — editing it would require the manual marketplace.json edit that
  release-plugin.mjs does not perform.

Tests 30 -> 42, all green. They are prose greps: drift guards, not proof the
ritual runs. Verifying that means a manual /graceful-handoff against a scratch
repo.

Release (tag + catalog ref bump) is operator-gated and NOT done here.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013V59bNbWa5x2oTH2NMBJy4

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "graceful-handoff",
-  "version": "3.1.0",
+  "version": "3.2.0",
   "description": "One-command session handoff into the STATE.md continuity system. /graceful-handoff reaches a natural stopping point, overwrites the nearest STATE.md with a complete state-of-play (mandatory '👉 NESTE' block), and commits per remote policy (private → tracked, public mirror → local-only). Skill-only, deterministic STATE helper, no hooks.",
   "author": {
     "name": "Kjell Tore Guttormsen"