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>

routes/task_routes.py

@@ -13,6 +13,7 @@ from pydantic import BaseModel
 from core.database import SessionLocal, ScheduledTask, TaskRun
 from core.constants import internal_api_base
 from src.auth_helpers import get_current_user
+from src.constants import DATA_DIR, EMAIL_URGENCY_CACHE_DIR
 from src.task_scheduler import compute_next_run, HOUSEKEEPING_DEFAULTS
 from routes.prefs_routes import _load_for_user, _save_for_user
 
@@ -621,7 +622,7 @@ def setup_task_routes(task_scheduler) -> APIRouter:
 
         removed_files = 0
         if action == "check_email_urgency":
-            cache_dir = Path("data/email_urgency_cache")
+            cache_dir = Path(EMAIL_URGENCY_CACHE_DIR)
             if cache_dir.exists():
                 for child in cache_dir.glob("*.json"):
                     try:
@@ -630,7 +631,7 @@ def setup_task_routes(task_scheduler) -> APIRouter:
                     except Exception:
                         pass
             owner_slug = "".join(c if (c.isalnum() or c in "-_.@") else "_" for c in (user or "default"))
-            for state_path in [Path(f"data/email_urgency_state_{owner_slug}.json")]:
+            for state_path in [Path(DATA_DIR) / f"email_urgency_state_{owner_slug}.json"]:
                 try:
                     if state_path.exists():
                         state_path.unlink()