feat: Unified Messaging System — kommunikation plugin, AI/Proactive/System participants, MessageSidebar, Rich Content Renderer

Phase 1: Backend plugin kommunikation (13 files, 10 tables, REST API, WebSocket, RBAC, DMS Bridge, Participant Registry, Mini-App Registry, Search Provider)
Phase 2: AI plugins as participants (ai_assistant + ai_proactive dock as participants, heartbeat job)
Phase 3: system_notif plugin (system events → chat messages, pinned System room)
Phase 4: Frontend MessageSidebar (replaces AISidebar, same design, comm API client, WebSocket hook, commStore)
Phase 5: Rich Content Block Renderer (11 components: Markdown, HTML, Image, Audio, Video, File, ActionCard, ContactCard, MiniApp, BlockRenderer)
BasePlugin: added services property + _container in on_activate

app/plugins/builtins/kommunikation/search_provider.py

@@ -0,0 +1,112 @@
+"""Search provider for unified_search integration."""
+
+from __future__ import annotations
+
+import logging
+import uuid
+from typing import Any
+
+from sqlalchemy import select, func, or_
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.plugins.builtins.kommunikation.models import (
+    CommConversation,
+    CommMessage,
+    CommParticipant,
+)
+
+logger = logging.getLogger(__name__)
+
+
+class CommSearchProvider:
+    """Provider for unified_search — searches conversations and messages."""
+
+    async def search(
+        self,
+        db: AsyncSession,
+        tenant_id: uuid.UUID,
+        user_id: uuid.UUID,
+        query: str,
+        limit: int = 20,
+    ) -> list[dict[str, Any]]:
+        """Search in messages and conversations the user has access to."""
+        results: list[dict[str, Any]] = []
+
+        # Get user's conversation IDs
+        conv_result = await db.execute(
+            select(CommParticipant.conversation_id).where(
+                CommParticipant.participant_id == user_id,
+                CommParticipant.participant_type == "user",
+                CommParticipant.left_at.is_(None),
+                CommParticipant.tenant_id == tenant_id,
+            )
+        )
+        conv_ids = [row[0] for row in conv_result.fetchall()]
+
+        if not conv_ids:
+            return results
+
+        # Search in messages
+        msg_result = await db.execute(
+            select(CommMessage, CommConversation.title)
+            .join(CommConversation, CommConversation.id == CommMessage.conversation_id)
+            .where(
+                CommMessage.conversation_id.in_(conv_ids),
+                CommMessage.tenant_id == tenant_id,
+                CommMessage.deleted_at.is_(None),
+                CommMessage.content.ilike(f"%{query}%"),
+            )
+            .order_by(CommMessage.created_at.desc())
+            .limit(limit)
+        )
+
+        for msg, conv_title in msg_result.fetchall():
+            # Build snippet around match
+            content = msg.content or ""
+            idx = content.lower().find(query.lower())
+            if idx >= 0:
+                start = max(0, idx - 30)
+                end = min(len(content), idx + len(query) + 30)
+                snippet = ("..." if start > 0 else "") + content[start:end] + ("..." if end < len(content) else "")
+            else:
+                snippet = content[:100]
+
+            results.append({
+                "type": "message",
+                "id": str(msg.id),
+                "conversation_id": str(msg.conversation_id),
+                "conversation_title": conv_title,
+                "content": msg.content,
+                "sender_type": msg.sender_type,
+                "created_at": msg.created_at.isoformat() if msg.created_at else None,
+                "snippet": snippet,
+            })
+
+        # Search in conversation titles
+        conv_title_result = await db.execute(
+            select(CommConversation).where(
+                CommConversation.id.in_(conv_ids),
+                CommConversation.tenant_id == tenant_id,
+                CommConversation.deleted_at.is_(None),
+                CommConversation.title.ilike(f"%{query}%"),
+            )
+            .limit(limit)
+        )
+
+        for conv in conv_title_result.scalars().all():
+            results.append({
+                "type": "conversation",
+                "id": str(conv.id),
+                "title": conv.title,
+                "last_msg_at": conv.last_msg_at.isoformat() if conv.last_msg_at else None,
+            })
+
+        return results
+
+    async def index_message(self, message: dict[str, Any]) -> None:
+        """Index a message for search (placeholder for future full-text indexing)."""
+        pass
+
+    async def reindex_all(self, db: AsyncSession, tenant_id: uuid.UUID) -> None:
+        """Full reindex (placeholder for future full-text indexing)."""
+        pass