fix: Restore all files lost during destructive rebase

A previous `git pull --rebase origin main` dropped 177 local commits,
losing 3400+ files across admin-v2, backend, studio-v2, website,
klausur-service, and many other services. The partial restore attempt
(660295e2) only recovered some files.

This commit restores all missing files from pre-rebase ref 98933f5e
while preserving post-rebase additions (night-scheduler, night-mode UI,
NightModeWidget dashboard integration).

Restored features include:
- AI Module Sidebar (FAB), OCR Labeling, OCR Compare
- GPU Dashboard, RAG Pipeline, Magic Help
- Klausur-Korrektur (8 files), Abitur-Archiv (5+ files)
- Companion, Zeugnisse-Crawler, Screen Flow
- Full backend, studio-v2, website, klausur-service
- All compliance SDKs, agent-core, voice-service
- CI/CD configs, documentation, scripts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

agent-core/sessions/__init__.py

@@ -0,0 +1,25 @@
+"""
+Session Management for Breakpilot Agents
+
+Provides:
+- AgentSession: Individual agent session with context and checkpoints
+- SessionManager: Create, retrieve, and manage agent sessions
+- HeartbeatMonitor: Monitor agent liveness
+- SessionState: Session state enumeration
+"""
+
+from agent_core.sessions.session_manager import (
+    AgentSession,
+    SessionManager,
+    SessionState,
+)
+from agent_core.sessions.heartbeat import HeartbeatMonitor
+from agent_core.sessions.checkpoint import CheckpointManager
+
+__all__ = [
+    "AgentSession",
+    "SessionManager",
+    "SessionState",
+    "HeartbeatMonitor",
+    "CheckpointManager",
+]