feat: v1.3.0 — plan-first workflow, OpenRouter provider, enhanced prompt engine

Major changes:
- Plan-first workflow: AI generates structured plan before code, with
  plan review card (Modify Plan / Start Coding / Skip to Code)
- Post-coding UX: Preview + Request Modifications buttons after code gen
- OpenRouter integration: 4th AI provider with 20+ model support
- Enhanced prompt engine: 9 strategies, 11+ intent patterns, modular
- PLAN MODE system prompt block in all 4 services
- Fixed stale React closure in approveAndGenerate with isApproval flag
- Fixed canvas auto-opening during plan phase with wasIdle gate
- Updated README, CHANGELOG, .env.example, version bump to 1.3.0

lib/store.ts

@@ -107,22 +107,26 @@ const useStore = create<AppState>((set) => ({
     qwen: "coder-model",
     ollama: "gpt-oss:120b",
     zai: "glm-4.7",
+    openrouter: "anthropic/claude-3.5-sonnet",
   },
   availableModels: {
     qwen: ["coder-model"],
     ollama: ["gpt-oss:120b", "llama3.1", "gemma3", "deepseek-r1", "qwen3"],
     zai: ["glm-4.7", "glm-4.6", "glm-4.5", "glm-4.5-air", "glm-4-flash", "glm-4-flashx"],
+    openrouter: ["anthropic/claude-3.5-sonnet", "google/gemini-2.0-flash-exp:free", "meta-llama/llama-3.3-70b-instruct", "openai/gpt-4o-mini", "deepseek/deepseek-chat-v3-0324", "qwen/qwen-2.5-72b-instruct"],
   },
   apiKeys: {
     qwen: "",
     ollama: "",
     zai: "",
+    openrouter: "",
   },
   githubToken: null,
   apiValidationStatus: {
     qwen: { valid: false },
     ollama: { valid: false },
     zai: { valid: false },
+    openrouter: { valid: false },
   },
   isProcessing: false,
   error: null,