feat(F): F-WORK agent_workstream + F-EMAIL/CONTACT/FOLLOW/REPORT prebuilt agents

- F-WORK: app/ai/agent_workstream.py (201 lines) — post_agent_message, post_agent_step, post_agent_result, post_approval_request
- F-EMAIL: prebuilt/email_triage_agent.py — E-Mail-Triage-Agent with 3 tools, max 10 steps, $0.50 budget
- F-CONTACT: prebuilt/contact_enrichment_agent.py — Contact-Enrichment-Agent with 3 tools, max 8 steps, $0.30 budget
- F-FOLLOW: prebuilt/follow_up_agent.py — Follow-up-Agent with 3 tools, max 8 steps, $0.30 budget
- F-REPORT: prebuilt/report_agent.py — Report-Agent with 2 tools, max 12 steps, $0.50 budget
- All compile checks pass

app/plugins/builtins/automation/prebuilt/follow_up_agent.py

@@ -0,0 +1,52 @@
+"""Pre-built Follow-up-Agent.
+
+Reminds about and creates follow-up tasks for contacts.
+"""
+from __future__ import annotations
+import uuid
+from app.plugins.builtins.automation.models import AgentDefinition
+
+FOLLOW_UP_SYSTEM_PROMPT = """You are a Follow-up Agent for a CRM system.
+
+Your task is to identify and create follow-up tasks for contacts.
+
+For each contact, you should:
+1. Check open tasks and calendar entries
+2. Review recent email communication
+3. Identify contacts that need follow-up (no response, overdue tasks, upcoming deadlines)
+4. Suggest follow-up actions (call, email, meeting, task)
+5. Create follow-up tasks when appropriate
+
+Use the available tools to:
+- Get open tasks (get_open_tasks)
+- Get contact emails (get_contact_mails)
+- Call CRM API for task creation (call_crm_api)
+
+Output format:
+- List of contacts needing follow-up with reason
+- Suggested action and timing for each
+- Priority level (urgent, this_week, this_month)
+
+You may create tasks via call_crm_api. Always include a clear description and due date.
+"""
+
+def create_follow_up_agent(
+    tenant_id: uuid.UUID, user_id: uuid.UUID
+) -> AgentDefinition:
+    return AgentDefinition(
+        tenant_id=tenant_id,
+        name="Follow-up-Agent",
+        description="Erstellt und erinnert an Follow-up-Tasks für Kontakte",
+        system_prompt=FOLLOW_UP_SYSTEM_PROMPT,
+        llm_model="openai/gpt-4o-mini",
+        tool_ids=["get_open_tasks", "get_contact_mails", "call_crm_api"],
+        max_steps=8,
+        max_duration_seconds=90,
+        budget_limit_usd=0.30,
+        mode="proactive",
+        is_active=True,
+        temperature=0.4,
+        max_tokens=1500,
+        trace_mode="standard",
+        created_by=user_id,
+    )