feat(career): career plugin — stars from song_stats, venue tiers, pack downloads (career mode PR2)

Bundled plugin: per-song stars from best_accuracy (60/75/85% → 1/2/3★),
cumulative stars unlock bar → club → arena (data-driven venues.json).
Venue packs (UE-rendered crowd loops) download on demand to
CONFIG_DIR/plugin_uploads/career/ on a background thread with sha256 +
zip-slip validation, served via FileResponse. Career screen (promoted
sidebar entry) shows progress and pushes the active venue's manifest
into the crowd video layer (v3VenueCrowd, PR1) — degrades cleanly when
either side is absent. Pack URLs land in venues.json in PR3.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/plugins/career/conftest.py

@@ -0,0 +1,64 @@
+import sqlite3
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent.parent.parent / 'plugins' / 'career'))
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+# Drop a sibling 'routes' cached by another plugin's tests (bare-name collision).
+sys.modules.pop('routes', None)
+import routes as career_routes
+
+
+class FakeMetaDb:
+    """song_stats-only stand-in for MetadataDB (the plugin reads nothing else)."""
+
+    def __init__(self):
+        self.conn = sqlite3.connect(":memory:", check_same_thread=False)
+        self.conn.execute(
+            """CREATE TABLE song_stats (
+                   filename TEXT, arrangement TEXT, best_accuracy REAL
+               )"""
+        )
+
+    def add(self, filename, arrangement, best_accuracy):
+        self.conn.execute("INSERT INTO song_stats VALUES (?, ?, ?)",
+                          (filename, arrangement, best_accuracy))
+        self.conn.commit()
+
+
+@pytest.fixture(autouse=True)
+def _bind_career_routes():
+    """Keep sys.modules['routes'] pointing at THIS plugin's routes for these tests."""
+    prev = sys.modules.get('routes')
+    sys.modules['routes'] = career_routes
+    try:
+        yield
+    finally:
+        if prev is not None:
+            sys.modules['routes'] = prev
+        else:
+            sys.modules.pop('routes', None)
+
+
+@pytest.fixture(autouse=True)
+def _reset_state():
+    # Module state outlives tests when the module stays imported — reset the
+    # mutable bits so ordering can't leak downloads/content between tests.
+    career_routes._state["downloads"] = {}
+    yield
+
+
+@pytest.fixture
+def meta_db():
+    return FakeMetaDb()
+
+
+@pytest.fixture
+def client(tmp_path, meta_db):
+    app = FastAPI()
+    career_routes.setup(app, {"config_dir": str(tmp_path), "meta_db": meta_db})
+    return TestClient(app)