feat: natural language skill routing + proactive suggestions (v0.7.1) (#195)

* feat: add trigger phrases to /debug and /office-hours

These two skills had zero "Use when asked to..." phrases, making them
completely invisible to natural language. Users saying "debug this" or
"brainstorm an idea" would get no skill invocation.

* feat: add proactive triggers to all workflow skills

Every skill now has "Proactively suggest when..." language so Claude
surfaces skills at natural moments — not just when the user says
specific trigger phrases.

* feat: lifecycle map + proactive preference system

Root gstack description now includes a developer workflow guide mapping
12 stages to skills. Preamble reads proactive preference via gstack-config.
Users can opt out with "stop suggesting things" and re-enable with
"be proactive again" — natural language toggle, no CLI needed.

* test: 11 journey-stage E2E routing tests + trigger phrase validation

Each test simulates a real development stage (ideation, plan review,
debug, QA, ship, retro...) with realistic project context and verifies
the right skill fires from natural language alone. 11/11 pass.

* chore: bump version and changelog (v0.7.1)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>