fix: address pre-merge review findings — stale identity strings, pyright error, fragile test path, formatting, README accuracy

Required fixes:
- main.py: update module docstring, startup comment, and FastAPI title from
  'tmux-web coordinator' / 'coordinator service' → 'muxplex' (4 locations)
- test_api.py: replace hasattr/BaseRoute pattern with isinstance(r, (APIRoute,
  APIWebSocketRoute)) to satisfy pyright (union-attr error eliminated)

Recommendations applied:
- test_api.py + test_cli.py: auto-formatted with ruff (blank-line normalisation)
- test_cli.py: replace exec(Path('muxplex/__main__.py').read_text()) with
  importlib.util.find_spec() to obtain the absolute path — no longer assumes
  pytest is invoked from a specific working directory
- README.md: fix architecture table — WebSocket proxy moved from ttyd.py
  description to main.py; ttyd.py now correctly described as lifecycle only

All 178 tests pass; python_check clean (0 errors, 0 warnings).

muxplex/tests/test_api.py

@@ -1,5 +1,5 @@
 """
-Tests for coordinator/main.py — FastAPI skeleton, lifespan, /health endpoint.
+Tests for muxplex/main.py — FastAPI skeleton, lifespan, /health endpoint.
 """
 
 import pytest
@@ -149,9 +149,7 @@ def test_patch_state_ignores_unknown_fields(client):
 def test_get_sessions_returns_list(client, monkeypatch):
     """GET /api/sessions must return a JSON list."""
     monkeypatch.setattr("muxplex.main.get_session_list", lambda: ["alpha"])
-    monkeypatch.setattr(
-        "muxplex.main.get_snapshots", lambda: {"alpha": "some text"}
-    )
+    monkeypatch.setattr("muxplex.main.get_snapshots", lambda: {"alpha": "some text"})
 
     response = client.get("/api/sessions")
     assert response.status_code == 200
@@ -210,9 +208,7 @@ def test_get_sessions_includes_bell_state(client, monkeypatch):
     from muxplex.state import save_state
 
     monkeypatch.setattr("muxplex.main.get_session_list", lambda: ["delta"])
-    monkeypatch.setattr(
-        "muxplex.main.get_snapshots", lambda: {"delta": "pane text"}
-    )
+    monkeypatch.setattr("muxplex.main.get_snapshots", lambda: {"delta": "pane text"})
     save_state(
         {
             "active_session": None,
@@ -647,9 +643,13 @@ def test_api_routes_not_shadowed(client):
 
 def test_terminal_ws_route_exists():
     """The app must have a WebSocket route registered at /terminal/ws."""
+    from fastapi.routing import APIRoute, APIWebSocketRoute
+
     from muxplex.main import app
+
     ws_routes = [
-        r for r in app.routes
-        if hasattr(r, "path") and r.path == "/terminal/ws"
+        r
+        for r in app.routes
+        if isinstance(r, (APIRoute, APIWebSocketRoute)) and r.path == "/terminal/ws"
     ]
     assert len(ws_routes) == 1, "Expected exactly one /terminal/ws route"