feat: edge prompt + session resume implementation (#402)

- buildContinuationPrompt: incremental prompt for role re-entry
- buildHermesPrompt: dual-mode (initial vs continuation)
- session-cache: thread:role → hermes sessionId mapping
- HermesAcpClient.resume(): session/resume JSON-RPC
- Fallback: cache miss or resume fail → initial prompt
- UWF_NO_RESUME env to skip cache
- solve-issue.yaml: reviewer→developer edge prompt
- Tests updated for EvaluateResult + continuation prompt

Refs #402

examples/solve-issue.yaml

@@ -62,14 +62,19 @@ graph:
   $START:
     - role: "planner"
       condition: null
+      prompt: null
   planner:
     - role: "developer"
       condition: null
+      prompt: null
   developer:
     - role: "reviewer"
       condition: null
+      prompt: null
   reviewer:
     - role: "developer"
       condition: "notApproved"
+      prompt: "The reviewer rejected your implementation. Read their feedback and fix the issues."
     - role: "$END"
       condition: null
+      prompt: null