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/architecture.md

@@ -0,0 +1,42 @@
+# Architecture
+
+<!--
+A response to the spec, not a setting. Written AFTER concept, users,
+requirements, NFR, IA, design system, interaction design, flows, and
+mocks are in place. Major decisions get their own ADR; this file is the
+summary + index.
+-->
+
+## Constraints (extracted from upstream artifacts)
+
+- <constraint> — *from <source>.md*
+- <constraint> — *from <source>.md*
+
+## Stack at a glance
+
+| Layer | Choice | ADR |
+|---|---|---|
+| Frontend | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+| Backend | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+| Data store | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+| Hosting / runtime | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+| Auth | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+| Observability | <…> | [ADR-NNNN](adr/NNNN-<slug>.md) |
+
+## Key architectural decisions
+
+<!--
+One bullet per ADR with the heart of the decision. Full reasoning lives
+in the ADR file.
+-->
+
+- **<Decision title>** — <one-line summary> ([ADR-NNNN](adr/NNNN-<slug>.md))
+
+## Open questions
+
+<!--
+Decisions deferred. Each should have a trigger condition that flips it
+into a real ADR.
+-->
+
+- <question> — *will decide when <trigger>*