Fix CACHE_DIR default path mismatch across files

Changed default from /data/cache to ~/.artdag/cache for local runs.
Docker sets CACHE_DIR=/data/cache via environment variable.

Files updated:
- tasks/analyze.py
- tasks/orchestrate.py
- app/config.py

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/config.py

@@ -19,9 +19,9 @@ class Settings:
     port: int = field(default_factory=lambda: int(os.environ.get("PORT", "8000")))
     debug: bool = field(default_factory=lambda: os.environ.get("DEBUG", "").lower() == "true")
 
-    # Cache
+    # Cache (use /data/cache in Docker via env var, ~/.artdag/cache locally)
     cache_dir: Path = field(
-        default_factory=lambda: Path(os.environ.get("CACHE_DIR", "/data/cache"))
+        default_factory=lambda: Path(os.environ.get("CACHE_DIR", str(Path.home() / ".artdag" / "cache")))
     )
 
     # Redis