Expose manage_notes via native function calling (#759)

The agent's RAG tool selector retrieves manage_notes as relevant for
note / todo / reminder requests, but two gaps stopped it from actually
firing on local llama.cpp / vLLM endpoints:

1. FUNCTION_TOOL_SCHEMAS had no entry for manage_notes. Even when the
   tool was marked relevant, no JSON schema was sent on the function
   tools list, so native-function-calling models had nothing to call.
   In practice the model would describe creating the note in prose
   while the actual note stayed blank — the symptom reported in #713
   ("checklist hallucinated as blank").

2. _API_HOSTS only listed hosted providers (OpenAI, Anthropic, etc.).
   For local endpoints like http://localhost:8080 or
   http://host.docker.internal:8000, _is_api_model fell back to
   keyword-sniffing the model name, so any model whose slug didn't
   happen to match the keyword list silently lost native tool
   schemas entirely.

Fixes:

- src/tool_schemas.py: add a manage_notes function schema covering
  list/add/update/delete/toggle_item with the full Keep-style field
  set. note_type is exposed as an enum ("note" | "checklist") so the
  model picks the mode explicitly instead of inferring it from
  content shape. Items are named checklist_items in the schema —
  consistent with the description's wording and avoiding the
  Python-built-in name clash that #713 calls out.

- src/tool_implementations.py: do_manage_notes accepts both
  checklist_items (new, schema-exposed) and items (legacy /
  internal). Direct API callers and existing code paths keep
  working unchanged; native function calls following the new
  schema route through the same path.

- src/agent_loop.py: add localhost, 127.0.0.1, and
  host.docker.internal to _API_HOSTS so the function-tool path is
  not gated behind model-name guessing for local servers.

Closes #174.
Closes #713.

src/tool_implementations.py

@@ -1853,7 +1853,13 @@ async def do_manage_notes(content: str, owner: Optional[str] = None) -> Dict:
                 title = text_raw.strip()
             elif not content_raw and text_raw:
                 content_raw = text_raw
-            items_raw = args.get("items")
+            # Accept both `items` (legacy/internal field) and `checklist_items`
+            # (the schema-exposed name used by native function calls). Models
+            # following the schema emit `checklist_items`; older code paths
+            # and direct API callers still use `items`.
+            items_raw = args.get("checklist_items")
+            if items_raw is None:
+                items_raw = args.get("items")
             items_json = json.dumps(items_raw) if items_raw is not None else None
             note_type = args.get("note_type", "checklist" if items_raw else "note")
             # Accept natural-language due_date ("tomorrow at 1pm") in
@@ -1918,8 +1924,11 @@ async def do_manage_notes(content: str, owner: Optional[str] = None) -> Dict:
             for field in ("title", "content", "note_type", "color", "label", "due_date"):
                 if field in args and args[field] is not None:
                     setattr(note, field, args[field])
-            if "items" in args and args["items"] is not None:
-                note.items = json.dumps(args["items"])
+            new_items = args.get("checklist_items")
+            if new_items is None:
+                new_items = args.get("items")
+            if new_items is not None:
+                note.items = json.dumps(new_items)
                 flag_modified(note, "items")
             if "pinned" in args:
                 note.pinned = args["pinned"]