feat(linkedin-studio): first-hour/reply-loop command with tracked state

Wire orphan agent #11 (engagement-coach) by giving it a command surface, and
add the tracked first-hour state the plan calls for (remediation Step 16).

- commands/firsthour.md (new, 27th command): post-publish first-hour /
  reply-loop sprint. Delegates plan construction to engagement-coach via
  Task (subagent_type: linkedin-studio:engagement-coach) — returns a grouped
  target list (whales/inner-circle/ICPs/new connections), 2-3 seed
  self-comments + 3-5 CEA replies in the user's voice, and a minute-by-minute
  timeline anchored to publish time. Presents timeline/targets/drafts +
  velocity checkpoints, auto-copies the drafts to clipboard, persists the
  plan, then hands off to post-feedback-monitor for the 48h window.
- hooks/scripts/state-updater.mjs: new pure mutation recordFirstHourPlan()
  mirroring updatePostTracking — additive by contract (inserts
  last_firsthour_date after last_post_date when absent, creates the
  ## First-Hour Plans section when absent, never touches existing fields).
  Section name is deliberately non-R-initial so it stays outside
  pruneContentHistory's "## Recent Posts ... (?=\n## [^R])" capture window.
  + a --record-firsthour CLI branch for parity with the other mutations.
- config/state-file.template.md: additive scalars (last_firsthour_date,
  firsthour_active) + the ## First-Hour Plans section.
- hooks/scripts/__tests__/state-updater.test.mjs: extend (existing file) with
  7 recordFirstHourPlan tests — section creation, field insertion vs in-place
  update (no duplication), round-trip non-interference, graceful empty
  defaults, changes array.
- CLAUDE.md: register the command (## Commands 26 -> 27, table row).
- scripts/test-runner.sh: EXPECT_COMMANDS 26 -> 27 (registration guard).

Verify: grep 'subagent_type: linkedin-studio:engagement-coach' commands/ ->
firsthour.md; node --test state-updater -> 26/26; full hook suite -> 83/83;
bash scripts/test-runner.sh -> exit 0 (62 passed, commands 27/27).

Plan Step 16 (Wave 4 S3).
[skip-docs]: tre-doc + version bump deferred to Step 21 per remediation plan.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugins/linkedin-studio/config/state-file.template.md

@@ -32,6 +32,10 @@ next_planned_topic: ""
 pending_5x5x5: false
 content_series_active: ""
 
+# First-hour / reply-loop engagement
+last_firsthour_date: null         # "YYYY-MM-DD HH:MM" of the most recent first-hour plan
+firsthour_active: false           # true while a first-hour loop is in progress
+
 # Profile
 expertise_areas:
   - "general"
@@ -59,3 +63,8 @@ expertise_areas:
 ## Milestone Log
 
 <!-- Updated when follower_count changes. Format: [YYYY-MM] count (+delta) -->
+
+## First-Hour Plans
+
+<!-- First-hour / reply-loop plans, newest first. Written by /linkedin:firsthour. -->
+<!-- Format: ### [YYYY-MM-DD HH:MM] topic -->