feat: initial BetonBLK project structure

BLOCKERS.md

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+# BetonBLK — Blockers
+
+## BLOCKER-001: Hosting Decision
+**Status:** OPEN
+**Impact:** Blocks deployment (Phase 3)
+**Options:**
+- Vercel — free tier, great for Next.js, limited backend
+- Railway — better for full-stack, Node.js native, $5/mo start
+**Decision needed by:** End of Phase 1
+**Owner:** Kev
+
+## BLOCKER-002: Auth Provider
+**Status:** OPEN
+**Impact:** Blocks user system (Feature 1.4+)
+**Options:**
+- Clerk — better DX, faster setup, more expensive at scale
+- Supabase Auth — already in stack, free tier generous, slightly more setup
+**Decision needed by:** Before Feature 1.4 implementation
+**Owner:** Kev