feat(product-shaping): add Shape Up adaptation skill for bounded product work

New class-level methodology skill adapted from Ryan Singer's Shape Up
(Basecamp, 2019), extended for human+AI-agent build teams:

- SKILL.md: core loop (shape -> bet -> build -> move on) with entry-point
  routing and negative trigger boundaries
- 6 references: principles, shaping (incl. non-UI work), betting, building,
  hybrid-adaptation, anti-patterns (independent field record 2019-2026)
- 2 templates: PITCH.md (five ingredients), SCOPE_MAP.md (hill states)
- evals: 6 output-quality cases incl. hybrid and routing regression cases

Routing surfaces: catalog README entry, skill-triggers index row,
product-methodology seam (consume won bets; no pre-bet shredding).
Generated artifacts regenerated against current main.

Closes #387

.claude-plugin/marketplace.json

@@ -950,6 +950,15 @@
       "strict": false,
       "description": "Build and maintain outcome-based product roadmaps and portfolio views that sequence strategic bets by evidence, not dates. Covers Now/Next/Later views, strategic-bet management, capacity allocation, dependency and confidence mapping, scenario planning, continue/pause/kill/revisit criteria, stakeholder narratives, and roadmap review cadences. Use when building or reviewing a product roadmap, managing a portfolio of bets, or communicating strategic sequencing to stakeholders. Do NOT use for tactical prioritization mechanics (RICE, MoSCoW, Kano, OST — route to product-methodology or product-strategy), for project scheduling or Gantt charts, or for delivery-flow management (route to kanban-guru)."
     },
+    {
+      "name": "product-shaping",
+      "source": "./",
+      "skills": [
+        "./product-shaping"
+      ],
+      "strict": false,
+      "description": "Use this skill to shape product or engineering work before committing time to it: set appetites instead of estimates, narrow raw ideas into bounded problems, sketch solutions at the right level of abstraction, de-risk rabbit holes, write pitches, bet with capped downside (circuit breaker), and govern builds with discovered scopes and scope hammering. Adapted from Basecamp's Shape Up and extended for human+AI-agent teams. Use when a raw idea, feature request, or \"redesign X\" grab-bag needs to become a bounded project before anyone builds; when planning how much work an idea is worth; or when delegated agent builds need budgets, kill criteria, and non-convergence rules. Do not use for discovering whether a problem is real (use product-discovery), for portfolio-level sequencing across quarters (product-roadmapping-and-portfolio), for formal specification after the bet is placed (spec-driven-development), or for task-level prioritization frameworks like RICE (product-methodology)."
+    },
     {
       "name": "product-strategy",
       "source": "./",