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/agent_loop.py

@@ -457,6 +457,11 @@ _API_HOSTS = frozenset([
     "api.together.xyz", "api.fireworks.ai",
     "api.perplexity.ai", "api.x.ai",
     "ollama.com",
+    # Local OpenAI-compatible endpoints (llama.cpp, vLLM, LM Studio, etc.).
+    # Without these, `_is_api_model` falls back to keyword sniffing on the
+    # model name, so well-behaved local servers don't get native tool
+    # schemas and the agent silently degrades to fenced-block parsing.
+    "localhost", "127.0.0.1", "host.docker.internal",
 ])
 _MCP_KEYWORDS = frozenset(["browse", "browser", "website", "calendar", "event", "email",
                            "gmail", "screenshot", "navigate", "click", "miniflux", "rss", "feed"])