Add milestone planning phase between /generate-app and /add-feature

- New command /plan-milestones: generates docs/milestones/ (roadmap.md + one document per milestone with its features, acceptance criteria, and ready-to-run /add-feature commands)
- New skill milestone-planning: MVP-first vertical-slice planning rules + milestone/roadmap templates
- /add-feature: reads the feature's milestone document before planning and checks the feature off (updating milestone/roadmap status) in Step 8
- Workflow diagrams, CLAUDE.md, README, and settings.json updated for the new phase

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.claude/skills/milestone-planning/template.md

@@ -0,0 +1,88 @@
+# Milestone Document Template
+
+Use this structure for each `docs/milestones/milestone-[NN]-[name].md`.
+
+```markdown
+# Milestone [NN]: [Name]
+
+**Status**: Not started | In progress | Completed
+**Goal**: [One sentence: what the user can do after this milestone that they could not before]
+
+## Scope
+
+### In Scope
+- [Theme or capability included in this milestone]
+
+### Out of Scope
+- [Explicitly excluded item] → [where it lives instead: milestone NN / icebox]
+
+## Dependencies
+
+- [What must exist before this milestone can start: previous milestone, external system, decision]
+
+## Features
+
+> One `/add-feature` run per feature. Check off each feature when its run completes.
+
+- [ ] [Feature 1 name]
+- [ ] [Feature 2 name]
+- [ ] [Feature 3 name]
+
+### Feature: [Feature 1 name]
+
+- **Description**: [What it does and the user value, 1–3 sentences]
+- **Related requirements**: [PRD user story / requirement IDs or headings]
+- **Affected screens**: [screen ids from ui-blueprint.json, or "n/a"]
+- **Acceptance criteria**:
+  - [Criterion 1]
+  - [Criterion 2]
+  - [Criterion 3]
+- **Command**: `/add-feature [Feature 1 name]`
+
+### Feature: [Feature 2 name]
+
+- **Description**: ...
+- **Related requirements**: ...
+- **Affected screens**: ...
+- **Acceptance criteria**:
+  - ...
+- **Command**: `/add-feature [Feature 2 name]`
+
+## Definition of Done
+
+- [ ] All features above are checked off
+- [ ] `npm test`, `npm run lint`, `npm run typecheck` pass
+- [ ] Persistent documents in `docs/` are reconciled with all features
+- [ ] [Milestone-specific criterion, e.g. "demo flow X→Y→Z works end-to-end"]
+
+## Completion Notes
+
+_Filled in when the milestone completes: completion date, deviations from plan, lessons learned._
+```
+
+# Roadmap Template
+
+Use this structure for `docs/milestones/roadmap.md`.
+
+```markdown
+# Development Roadmap
+
+**Current milestone**: [NN — name]
+
+## Milestones
+
+| # | Name | Goal | Features | Status |
+|---|------|------|----------|--------|
+| 01 | [name] | [one-line goal] | [count] | Not started / In progress / Completed |
+| 02 | [name] | [one-line goal] | [count] | Not started |
+
+## Ordering Rationale
+
+[Why this sequence: MVP definition, dependency chains, priority decisions made with the user]
+
+## Later / Icebox
+
+Consciously deferred — revisit when re-planning:
+
+- [Deferred item] — [why deferred]
+```