Let the operator drop unused tools from the MCP surface

[raphasouthall]

Closes #122.

What

disabled_tools in config.toml, plus a NEUROSTACK_DISABLED_TOOLS env override, naming tools to leave off the MCP surface. create_mcp_server skips them when registering.

Why

Every registered tool's schema is injected into every client session, so a tool nobody calls costs tokens on each turn and lengthens the menu the model picks from. Counting real calls across 48 local sessions, 12 of the 29 tools have never been called once — roughly 1.2k tokens of dead schema per session. Neither Claude Code nor omp exposes a per-tool MCP filter, so the choice has to live server-side.

How

• Config.disabled_tools: list[str], empty by default, so behaviour is unchanged for anyone who sets nothing.
• The TOML parser accepts a list or a string, since a hand-edited config is as likely to hold "a, b" as ["a", "b"].
• NEUROSTACK_DISABLED_TOOLS takes comma- or space-separated names and replaces the file value rather than merging, matching how every other env override in load_config behaves.
• The adapter logs which tools it skipped, and warns on a name matching no tool so a typo shows up in the log instead of silently disabling nothing.

Gate

uv run ruff check src/ tests/ exit 0. uv run pytest -q exit 0, 834 passed (+6).

New tests cover the default staying empty, the TOML list, the TOML string being split, env beating TOML, the adapter omitting a disabled tool while keeping the rest, and the adapter registering everything when the list is empty.