feat: proactive skill suggestions + opt-out + trigger phrase tests

- Preamble reads proactive config via gstack-config
- Root SKILL.md.tmpl has lifecycle map (stage → skill suggestion)
- Users can opt out ("stop suggesting") / opt in ("be proactive again")
- Restored trigger phrase validation tests (16 skills × "Use when" check)
- Added missing "Use when" trigger phrases to /debug and /office-hours

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

debug/SKILL.md

@@ -4,6 +4,8 @@ version: 1.0.0
 description: |
   Systematic debugging with root cause investigation. Four phases: investigate,
   analyze, hypothesize, implement. Iron Law: no fixes without root cause.
+  Use when asked to "debug this", "fix this bug", "why is this broken",
+  "investigate this error", or "root cause analysis".
 allowed-tools:
   - Bash
   - Read
@@ -26,8 +28,10 @@ touch ~/.gstack/sessions/"$PPID"
 _SESSIONS=$(find ~/.gstack/sessions -mmin -120 -type f 2>/dev/null | wc -l | tr -d ' ')
 find ~/.gstack/sessions -mmin +120 -type f -delete 2>/dev/null || true
 _CONTRIB=$(~/.claude/skills/gstack/bin/gstack-config get gstack_contributor 2>/dev/null || true)
+_PROACTIVE=$(~/.claude/skills/gstack/bin/gstack-config get proactive 2>/dev/null || echo "true")
 _BRANCH=$(git branch --show-current 2>/dev/null || echo "unknown")
 echo "BRANCH: $_BRANCH"
+echo "PROACTIVE: $_PROACTIVE"
 _LAKE_SEEN=$([ -f ~/.gstack/.completeness-intro-seen ] && echo "yes" || echo "no")
 echo "LAKE_INTRO: $_LAKE_SEEN"
 ```

debug/SKILL.md.tmpl

@@ -4,6 +4,8 @@ version: 1.0.0
 description: |
   Systematic debugging with root cause investigation. Four phases: investigate,
   analyze, hypothesize, implement. Iron Law: no fixes without root cause.
+  Use when asked to "debug this", "fix this bug", "why is this broken",
+  "investigate this error", or "root cause analysis".
 allowed-tools:
   - Bash
   - Read