Refactor: split serve/server.py (3220 lines) into focused modules

serve/server.py is now 69 lines — app factory, middleware, and router
registration only.

New modules:
  deps.py    (168 lines) — module-level globals + auth dependency functions
  models.py   (85 lines) — all Pydantic request/response models
  tasks.py   (136 lines) — background workers and job tracker
  routers/               — one file per domain (10 routers, ~2750 lines total)
    auth.py, me.py, admin.py, activities.py, uploads.py,
    segments.py, strava.py, garmin.py, ideas.py, feed.py

cli.py updated to set globals on deps instead of server.

88 new regression tests in tests/serve/ cover auth guards and key
behaviours for every router; 294 total passing after the split.

tests/serve/conftest.py

@@ -0,0 +1,81 @@
+"""Shared fixtures for serve/ router tests.
+
+The fixture patches data_dir on whichever module owns it — works against
+both the pre-split monolith (bincio.serve.server) and the post-split
+layout (bincio.serve.deps).
+"""
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from fastapi.testclient import TestClient
+
+from bincio.serve.db import create_session, create_user, open_db
+
+
+def _set_data_dir(path: Path) -> None:
+    try:
+        import bincio.serve.deps as deps
+        deps.data_dir = path
+        deps._db = None
+    except (ImportError, AttributeError):
+        import bincio.serve.server as srv
+        srv.data_dir = path
+        srv._db = None
+
+
+def _get_data_dir() -> Path | None:
+    try:
+        import bincio.serve.deps as deps
+        return deps.data_dir
+    except (ImportError, AttributeError):
+        import bincio.serve.server as srv
+        return srv.data_dir
+
+
+@pytest.fixture()
+def tmp_data(tmp_path: Path) -> Path:
+    """Return a tmp_path with a valid instance.db."""
+    open_db(tmp_path)   # creates schema
+    return tmp_path
+
+
+@pytest.fixture()
+def client(tmp_data: Path) -> TestClient:
+    from bincio.serve.server import app
+    _set_data_dir(tmp_data)
+    return TestClient(app, raise_server_exceptions=False)
+
+
+@pytest.fixture()
+def admin_client(tmp_data: Path) -> TestClient:
+    """Client with an admin session cookie pre-set."""
+    from bincio.serve.server import app
+    _set_data_dir(tmp_data)
+
+    db = open_db(tmp_data)
+    create_user(db, "admin", "Admin", "adminpass1", is_admin=True,
+                wiki_access=True, activity_access=True)
+    token = create_session(db, "admin")
+
+    c = TestClient(app, raise_server_exceptions=False)
+    c.cookies.set("bincio_session", token)
+    return c
+
+
+@pytest.fixture()
+def user_client(tmp_data: Path) -> TestClient:
+    """Client with a regular (non-admin) session cookie pre-set."""
+    from bincio.serve.server import app
+    _set_data_dir(tmp_data)
+
+    db = open_db(tmp_data)
+    create_user(db, "alice", "Alice", "alicepass1", is_admin=False,
+                wiki_access=True, activity_access=True)
+    (tmp_data / "alice" / "activities").mkdir(parents=True, exist_ok=True)
+    token = create_session(db, "alice")
+
+    c = TestClient(app, raise_server_exceptions=False)
+    c.cookies.set("bincio_session", token)
+    return c