fix: resolve all 28 mypy type errors + re-enable coverage in CI

backend/main.py

@@ -583,8 +583,8 @@ from backend.audit import log_file_save, log_file_delete  # noqa: E402
 try:
     from backend.pdf_export import generate_pdf, build_pdf_html  # noqa: E402
 except OSError:
-    generate_pdf = None
-    build_pdf_html = None
+    generate_pdf = None  # type: ignore[assignment]
+    build_pdf_html = None  # type: ignore[assignment]
     import logging
     logging.getLogger("obsigate").warning("PDF export unavailable (WeasyPrint/GTK not found)")
 from backend.share import create_share, get_share_by_token, record_access, revoke_share, list_shares  # noqa: E402
@@ -1026,7 +1026,7 @@ async def api_toggle_bookmark(req: BookmarkToggleRequest, current_user=Depends(r
     if not check_vault_access(req.vault, current_user):
         raise HTTPException(status_code=403, detail="Access denied to vault")
         
-    is_now_bookmarked = toggle_bookmark(username, req.vault, req.path, req.title)
+    is_now_bookmarked = toggle_bookmark(username, req.vault, req.path, req.title or "")
 
     # Update the file's YAML frontmatter: favoris: true/false
     vault_data = get_vault_data(req.vault)
@@ -3063,6 +3063,10 @@ async def api_conflict_resolve(body: dict = Body(...), current_user=Depends(requ
     conflict_path = body.get("conflict_path")
     original_path = body.get("original_path")
     action = body.get("action")  # "keep_local" or "keep_conflict"
+    # mypy: narrow down from dict values
+    assert isinstance(vault_name, str), "'vault' is required and must be a string"
+    assert isinstance(conflict_path, str), "'conflict_path' is required and must be a string"
+    assert isinstance(original_path, str), "'original_path' is required and must be a string"
     if not check_vault_access(vault_name, current_user):
         raise HTTPException(403, f"Accès refusé à la vault '{vault_name}'")
     vault_data = get_vault_data(vault_name)