fix: prevent temp file accumulation during long agent runs

Address three issues reported after overnight AutoForge runs:
1. ~193GB of .node files in %TEMP% from V8 compile caching
2. Stale npm artifact folders on drive root when %TEMP% fills up
3. PNG screenshot files left in project root by Playwright

Changes:
- Widen .node cleanup glob from ".78912*.node" to ".[0-9a-f]*.node"
  to match all V8 compile cache hex prefixes
- Add "node-compile-cache" directory to temp cleanup patterns
- Set NODE_COMPILE_CACHE="" in all subprocess environments (client.py,
  parallel_orchestrator.py, process_manager.py) to disable V8 compile
  caching at the source
- Add cleanup_project_screenshots() to remove stale .png files from
  project directories (feature*-*.png, screenshot-*.png, step-*.png)
- Run cleanup_stale_temp() at server startup in lifespan()
- Add _run_inter_session_cleanup() to orchestrator, called after each
  agent completes (both coding and testing paths)
- Update coding and testing prompt templates to instruct agents to use
  inline (base64) screenshots only, never saving files to disk

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/services/process_manager.py

@@ -410,6 +410,7 @@ class AgentProcessManager:
                 **os.environ,
                 "PYTHONUNBUFFERED": "1",
                 "PLAYWRIGHT_HEADLESS": "true" if playwright_headless else "false",
+                "NODE_COMPILE_CACHE": "",  # Disable V8 compile caching to prevent .node file accumulation in %TEMP%
                 **api_env,
             }