feat: remove trigger guard + proactive opt-out prompt

Remove "MANUAL TRIGGER ONLY" injection from all skill descriptions. This
frees 59 chars per skill from the 1024-char Codex description budget and
lets skills auto-fire based on semantic matching.

Merge auto-fire control into the existing `proactive` setting — when false,
Claude won't auto-invoke skills or suggest them. Users are prompted once
about this preference (chains after the telemetry prompt, fires on second
skill run).

Also trims the root gstack description by removing the skill catalog
(already in the body), saving ~500 chars.

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

SKILL.md.tmpl

@@ -7,14 +7,6 @@ description: |
   elements, verify state, diff before/after, take annotated screenshots, test responsive
   layouts, forms, uploads, dialogs, and capture bug evidence. Use when asked to open or
   test a site, verify a deployment, dogfood a user flow, or file a bug with screenshots.
-  Also suggest adjacent gstack skills by stage: brainstorm /office-hours; strategy
-  /plan-ceo-review; architecture /plan-eng-review; design /plan-design-review or
-  /design-consultation; auto-review /autoplan; debugging /investigate; QA /qa; code review
-  /review; visual audit /design-review; shipping /ship; docs /document-release; retro
-  /retro; second opinion /codex; prod safety /careful or /guard; scoped edits /freeze or
-  /unfreeze; gstack upgrades /gstack-upgrade. If the user opts out of suggestions, stop
-  and run gstack-config set proactive false; if they opt back in, run gstack-config set
-  proactive true.
 allowed-tools:
   - Bash
   - Read