feat: first-run activation — project-aware scaffold, router front door, onboarding nudges

Adds the activation system that drives a new install toward a concrete first move:
- bin/gstack-first-task-detect: local-git+filesystem repo classifier emitting one
  validated enum bucket (greenfield/code_<lang>/branch_ahead/dirty_default/clean_default),
  portable timeouts, fail-safe empty output.
- generate-first-run-guidance.ts: unified preamble section — first-run project-aware
  scaffold + returning-session plan->review->ship tip, gated on a persistent .activated
  marker and never run in headless. Detection wired lazily in generate-preamble-bash.ts.
- SKILL.md.tmpl: top-level gstack skill is now a pure router (browse body removed; it
  lives in /browse), routing any request and sending browser/QA work to /browse.
- setup: first-move nudge on first install. office-hours: closing handoff that launches
  the next review via the Skill tool.
- telemetry-ingest: accept onboarding/first_task_scaffold_shown/handoff/route event types.

scripts/resolvers/preamble/generate-preamble-bash.ts

@@ -43,6 +43,17 @@ echo "SESSION_KIND: $_SESSION_KIND"
 if [ "$_SESSION_KIND" != "headless" ] && { [ -n "\${CONDUCTOR_WORKSPACE_PATH:-}" ] || [ -n "\${CONDUCTOR_PORT:-}" ]; }; then
   echo "CONDUCTOR_SESSION: true"
 fi
+_ACTIVATED=$([ -f ~/.gstack/.activated ] && echo "yes" || echo "no")
+_FIRST_LOOP_SHOWN=$([ -f ~/.gstack/.first-loop-tip-shown ] && echo "yes" || echo "no")
+echo "ACTIVATED: $_ACTIVATED"
+echo "FIRST_LOOP_SHOWN: $_FIRST_LOOP_SHOWN"
+# First-run project detection: run the detector ONLY on the first-ever skill run
+# (ACTIVATED=no, interactive) so it stays off the hot path for every run after.
+_FIRST_TASK=""
+if [ "$_ACTIVATED" = "no" ] && [ "$_SESSION_KIND" != "headless" ]; then
+  _FIRST_TASK=$(${ctx.paths.binDir}/gstack-first-task-detect 2>/dev/null || true)
+fi
+echo "FIRST_TASK: $_FIRST_TASK"
 _LAKE_SEEN=$([ -f ~/.gstack/.completeness-intro-seen ] && echo "yes" || echo "no")
 echo "LAKE_INTRO: $_LAKE_SEEN"
 _TEL=$(${ctx.paths.binDir}/gstack-config get telemetry 2>/dev/null || true)