feat(composer): discovery-phase plugin from "I want an app that..." to tracker-loaded stories

Plugin pairs with Symphony — Composer's output (issues in the project's
tracker) is Symphony's input. State-aware /composer command walks the
user through 11 phases: concept, users (with workflow probing for hidden
actors), requirements/NFR/IA, design system, interaction design, flows,
mocks, architecture, stories, roadmap, load. Each phase produces a
reviewable artifact in docs/planning/ (or, for design and interaction,
a project-local skill — see below).

Architecture is intentionally LAST, after the spec is complete. Mocks
are JSX/TSX regardless of final stack and pass a "text feasibility"
audit — every visible string is categorized (static/computed/authored),
computed strings are traced to source data, and any string implying an
unspecified feature halts the commit.

Design system and interaction design are produced as PROJECT-LOCAL
SKILLS in .claude/skills/<slug>-design-system/ and
.claude/skills/<slug>-interaction-design/, not as docs in
docs/planning/. Skills auto-load via description matching whenever UI
work happens; a reference doc gets read once and drifts out of context.
The mocks skill imports tokens directly from the design-system skill
for a single source of truth across mocks and (eventually) real code.

ui-system is currently a PLACEHOLDER — captures the minimum needed for
mocks to proceed with <TBD: ...> markers as a return-pass worklist.
Full interview specification is the next pass.

Council touchpoints baked in: PM/skeptic/end-user after requirements,
end-user/a11y after mocks, full architecture council after architecture,
plus auto-additions (legal-triage on regulated data, privacy-advocate
on PII, finance-controller on money flows).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

composer/templates/planning-pointers/interaction-design.md

@@ -0,0 +1,18 @@
+# Interaction design
+
+The interaction-design system for this project is implemented as a
+project skill so it loads automatically into context whenever UI behavior
+is being built (modals, forms, transitions, error states, focus, etc.).
+
+**Skill location**: `.claude/skills/<SLUG>-interaction-design/`
+
+```
+.claude/skills/<SLUG>-interaction-design/
+└── SKILL.md   ← state surfaces, motion, input modes, i18n, state postures
+```
+
+To revise: re-run `/composer`, or edit the SKILL.md directly. It's
+version-controlled.
+
+The paired design-system skill lives at
+`.claude/skills/<SLUG>-design-system/`.