feat(FN-1984): enrich chat and heartbeat prompts with agent context

- Add agent memory support to instruction resolution and introduce/export buildAgentChatPrompt for identity-aware prompt assembly with optional project memory
- Wire ChatManager to AgentStore so chat sessions can enrich system prompts per agent and include recent conversation context in prompt payloads
- Update server chat wiring to provide an AgentStore for prompt enrichment and keep graceful fallback behavior when agent context is unavailable
- Enrich HeartbeatMonitor system prompts with resolved agent instructions/ratings while preserving base-prompt fallback paths
- Expand dashboard and engine tests to cover prompt enrichment, fallback behavior, conversation context assembly, and AgentStore route mocks

packages/engine/src/index.ts

@@ -26,6 +26,12 @@ export {
   type SkillDiagnostic,
 } from "./skill-resolver.js";
 export { AgentReflectionService, type AgentReflectionServiceOptions } from "./agent-reflection.js";
+export {
+  buildAgentChatPrompt,
+  resolveAgentInstructionsWithRatings,
+  resolveAgentInstructions,
+  buildSystemPromptWithInstructions,
+} from "./agent-instructions.js";
 export { WorktreePool, scanIdleWorktrees, cleanupOrphanedWorktrees } from "./worktree-pool.js";
 export { createLogger, type Logger } from "./logger.js";
 export { isUsageLimitError, UsageLimitPauser } from "./usage-limit-detector.js";