config: add OpenCode API fallback for Gemini quota

- Configured OpenCode as fallback when Gemini quota exceeded
- Created gemini-fallback.js utility (tries Gemini → OpenCode)
- API keys stored in .env (excluded from git)
- PM unblocked: can resume 05-03 with fallback system

Flow: Gemini (primary) → OpenCode (fallback) → fail gracefully

.pm-checkpoint.json

@@ -1,7 +1,26 @@
 {
-  "lastRun": "2026-03-02T18:20:00Z",
-  "status": "completed",
-  "result": "Task 05-03 completed: Frontend integration for exercise research display. Created ExerciseResearchPanel.jsx (107 lines) and ExerciseEncyclopediaPage.jsx (128 lines). Wired into App.jsx with nav button and CSS.",
-  "nextTask": "05-04: Testing and polish (if any remaining tasks in phase 05)",
-  "commits": ["83ccd6c feat(05-03): Exercise research frontend integration"]
+  "lastRun": "2026-03-02T19:37:00Z",
+  "status": "unblocked",
+  "unblockedReason": "OpenCode API configured as fallback for Gemini quota",
+  "currentPhase": "05",
+  "currentTask": "05-03",
+  "result": "Fallback system implemented: Gemini (primary) → OpenCode (fallback)",
+  "nextTask": "05-03: Frontend integration for research display (can now proceed with OpenCode fallback)",
+  
+  "apiConfiguration": {
+    "primary": {
+      "provider": "Gemini",
+      "status": "quota-limited",
+      "notes": "Free tier has daily limits"
+    },
+    "fallback": {
+      "provider": "OpenCode",
+      "baseUrl": "https://api.opencode.com/v1",
+      "model": "gpt-4",
+      "status": "configured"
+    },
+    "implementation": "backend/src/utils/gemini-fallback.js"
+  },
+  
+  "action": "READY TO RESUME: PM can continue with 05-03 using fallback"
 }