Remove /generate-app: app shell is now milestone 01 of the plan

The initial app is no longer generated by a separate command. /plan-milestones
now always makes milestone 01 'App Shell Generation' (target platform asked in
the single question round): theme from design tokens, one screen per blueprint
entry, routes, reusable components — no feature logic — plus Playwright setup
and the e2e/app-shell.spec.ts smoke spec. It is executed like any other
milestone via /execute-milestones (which follows platform-ui-generation for it)
or /add-feature. Milestone 02 becomes the MVP core. All workflow diagrams,
skills, docs READMEs, AGENTS.md, and README updated; docs/design README also
gains the screen-inventory.md entry.

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

.opencode/command/execute-milestones.md

@@ -30,8 +30,6 @@ opencode
   ↓
 /define-design
   ↓
-/generate-app web | flutter | winui3
-  ↓
 /plan-milestones
   ↓
 /execute-milestones phase1-milestones.md   ← you are here (one phase file per run)
@@ -59,6 +57,7 @@ opencode
 
 1. Follow the **milestone-execution** skill (loaded automatically) for the per-milestone steering structure, task-division rules, and the gate criteria between milestones.
 2. The **steering** and **development-guidelines** skills apply during implementation, exactly as in `/add-feature`.
+3. **If the milestone is the App Shell milestone (milestone 01)**, additionally follow the **platform-ui-generation** skill (loaded automatically) for the design→code mapping rules of the target platform recorded in the milestone. Its E2E verification is the `e2e/app-shell.spec.ts` smoke spec (shell renders, every blueprint route navigates).
 
 ### Step 2: Milestone Loop