Add profile-driven feature runtime utilities

- Add feature_registry.py with FeatureGroup definitions for core, podcast, youtube, content_planning
- Add feature_profiles.py to parse ALWRITY_FEATURE_TO_ENABLE env var
- Add feature_runtime.py with is_enabled(), get_enabled_routers() helpers
- Fix syntax error in __init__.py (duplicate OnboardingManager)

Enables feature toggles via ALWRITY_FEATURE_TO_ENABLE environment variable.

backend/alwrity_utils/feature_registry.py

@@ -0,0 +1,63 @@
+"""Feature registry for profile-based capability toggles.
+
+This module stores normalized feature-group definitions used by the
+feature profile runtime.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Dict, Tuple
+
+
+@dataclass(frozen=True)
+class FeatureGroup:
+    """Single feature group and the capabilities it enables."""
+    
+    routers: Tuple[str, ...] = ()
+    startup_hooks: Tuple[str, ...] = ()
+    optional_services: Tuple[str, ...] = ()
+    features: Tuple[str, ...] = field(default_factory=tuple)
+
+
+FEATURE_GROUPS: Dict[str, FeatureGroup] = {
+    "core": FeatureGroup(
+        features=("core", "health", "onboarding", "research"),
+        routers=(
+            "api.component_logic:router",
+            "api.subscription:router",
+            "api.onboarding_utils.step3_routes:router",
+            "api.research.router:router",
+        ),
+        startup_hooks=(
+            "services.database:init_database",
+        ),
+        optional_services=(
+            "services.scheduler:get_scheduler",
+        ),
+    ),
+    "podcast": FeatureGroup(
+        features=("podcast",),
+        routers=("api.podcast.router:router",),
+    ),
+    "youtube": FeatureGroup(
+        features=("youtube",),
+        routers=("api.youtube.router:router",),
+    ),
+    "content_planning": FeatureGroup(
+        features=("content_planning", "strategy_copilot"),
+        routers=(
+            "api.content_planning.api.router:router",
+            "api.content_planning.strategy_copilot:router",
+        ),
+    ),
+}
+
+
+PROFILE_GROUP_MAP: Dict[str, Tuple[str, ...]] = {
+    "all": tuple(FEATURE_GROUPS.keys()),
+    "core": ("core",),
+    "podcast": ("core", "podcast"),
+    "youtube": ("core", "youtube"),
+    "planning": ("core", "content_planning"),
+}