Tighten snapshot/window models, typed packaging marker, and protocol docs

[tony]

Problem

Several small public-surface gaps make the server less ergonomic and less accurate for MCP clients.

Grouped here because each fix is small and independently testable.

Items

1. snapshot_pane should include important tmux state:

   • pane_pid
   • pane_dead
   • alternate_on

2. WindowInfo should include active_pane_id, matching the convenience already present on SessionInfo.

3. The package advertises typed distribution but does not ship py.typed.

4. README's tool table is stale and misses current tools such as:

   • list_servers
   • wait_for_channel
   • signal_channel
   • buffer tools
   • hook inspection tools

5. Completion docs describe inherited completion behavior, but a real completion/complete request currently returns Method not found.

6. Pagination docs say protocol list calls return nextCursor, but this server does not configure list_page_size.

7. Prompt docs say run_and_wait preserves exit status, then later say it does not.

Upstream references

• tmux exposes alternate_on: https://github.com/tmux/tmux/blob/3.6a/format.c#L3148-L3149
• tmux exposes pane_dead: https://github.com/tmux/tmux/blob/3.6a/format.c#L3391-L3392
• tmux exposes pane_pid: https://github.com/tmux/tmux/blob/3.6a/format.c#L3457-L3458
• FastMCP pagination is opt-in via list_page_size: https://github.com/jlowin/fastmcp/blob/v3.4.2/fastmcp_slim/fastmcp/server/server.py#L311-L368
• FastMCP emits nextCursor when pagination is configured: https://github.com/jlowin/fastmcp/blob/v3.4.2/fastmcp_slim/fastmcp/server/mixins/mcp_operations.py#L117-L186

Minimal local recreation

Check current server surface:

$ uv run fastmcp inspect fastmcp.json

Check completion behavior:

$ uv run python - <<'PY'
import asyncio
from fastmcp import Client
from mcp import types
from libtmux_mcp.server import build_mcp_server

async def main():
    async with Client(build_mcp_server()) as client:
        await client.complete(
            types.PromptReference(type="ref/prompt", name="run_and_wait"),
            {"name": "command", "value": "py"},
        )

asyncio.run(main())
PY

Expected today: McpError Method not found.

Minimal fix

• Add only the three snapshot fields listed above.
• Add active_pane_id to WindowInfo.
• Add src/libtmux_mcp/py.typed.
• Regenerate or manually update the README tool inventory.
• Rewrite completion and pagination docs to describe current behavior.
• Fix the run_and_wait exit-status sentence.

Acceptance criteria

• snapshot_pane returns pane_pid, pane_dead, and alternate_on.
• create_window / WindowInfo includes active_pane_id.
• Built wheel/sdist includes libtmux_mcp/py.typed.
• README tool inventory matches tools/list.
• Completion docs no longer claim a working completion/complete surface.
• Pagination docs distinguish FastMCP capability from this server's current configuration.
• Prompt docs consistently state that run_and_wait does not preserve exit status.