refactor(constants): single source of truth for data dir (#3368)

* refactor(constants): single source of truth for data dir + merge core/src constants

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(contributing): use named src.constants for data paths, drop core/constants references

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ai_interaction.py

@@ -14,6 +14,8 @@ import uuid
 import time
 from typing import Dict, Optional, Tuple
 
+from src.constants import GENERATED_IMAGES_DIR
+
 logger = logging.getLogger(__name__)
 
 AI_CHAT_TIMEOUT = 120  # seconds for a single LLM call
@@ -1715,7 +1717,7 @@ async def do_generate_image(content: str, session_id: Optional[str] = None, owne
 
             # GPT image models always return b64_json; DALL-E may return url
             if img.get("b64_json"):
-                img_dir = Path("data/generated_images")
+                img_dir = Path(GENERATED_IMAGES_DIR)
                 img_dir.mkdir(parents=True, exist_ok=True)
                 filename = f"{uuid.uuid4().hex[:12]}.png"
                 img_path = img_dir / filename
@@ -1728,7 +1730,7 @@ async def do_generate_image(content: str, session_id: Optional[str] = None, owne
                 try:
                     dl_resp = httpx.get(img["url"], timeout=60)
                     if dl_resp.status_code == 200:
-                        img_dir = Path("data/generated_images")
+                        img_dir = Path(GENERATED_IMAGES_DIR)
                         img_dir.mkdir(parents=True, exist_ok=True)
                         filename = f"{uuid.uuid4().hex[:12]}.png"
                         img_path = img_dir / filename