chore(oss): move internal planning docs out of the public tree

docs/ keeps design.md (architecture) and cost-methodology.md (scoring
math); internal milestone plans and strategy notes are maintained
privately. References updated.

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

Author: yunhao-j

app/changelog/ChangelogClient.tsx

@@ -75,14 +75,14 @@ const ENTRIES: Entry[] = [
   {
     date: '2026-05-26',
     tag: 'platform',
-    title: 'Plan rewrite + multi-event / multi-agent / live architecture (codercup-v1)',
+    title: 'Plan rewrite + multi-event / multi-agent / live architecture',
     body: (
       <>
         The original codearena-v1 plan assumed one launch event (World Cup
         2026, hard date 6/22). Reality drifted: the brand changed, the
         launch model went continuous, and the site grew surfaces the plan
         never anticipated. After a self-audit, the plan was rewritten as{' '}
-        <code>docs/codercup-v1/</code> with three independent axes treated
+        a revised build plan with three independent axes treated
         as first-class concepts (event / agent / live), each piece scoped
         90/10, deferred work surfaced via{' '}
         <code>coming-soon-pattern.md</code>. Phase 1 ships:

app/lib/api.ts

@@ -87,7 +87,7 @@ export interface AgentJson {
   runs: RunSummary[];
 }
 
-// ─── Event schema (codercup-v1 m2 piece-1 · v2 — event-centric) ───────────
+// ─── Event schema (v2 — event-centric) ─────────────────────────────────────
 
 export type EventState = 'planning' | 'dry-run' | 'live' | 'completed' | 'archived';