feat(agents): reset button + endpoint to clear stuck agent error state

Adds a one-click 'reset agents' action for cases where writer/QA agents
are stuck in Paperclip's error state (triggered by recovery loop or
failed run). Addresses the root cause documented in
reference_paperclip_recovery_loops: reassigns open issues from agents
back to the chair user, and calls reset_agent_session for each error
agent to clear wedged runtime sessions.

Changes:
- paperclip_client.py: reset_case_agents() — reassigns stuck issues +
  clears error status in Paperclip DB + calls reset_agent_session
- agent_platform_port.py: exports pc_reset_case_agents (G12 gate)
- app.py: POST /api/cases/{case_number}/agents/reset endpoint
- agents.ts: useResetCaseAgents mutation hook + AgentResetResult type
- agent-status-widget.tsx: 'אפס' button (shown only when error agents
  exist) with Dialog confirmation + loading state + toast feedback

Invariants: G12 (Paperclip only via port), G2 (no parallel path —
uses existing reset_agent_session + pc_get_case_issues).

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

web/app.py

@@ -72,6 +72,7 @@ from web.agent_platform_port import (
     pc_reject_interaction,
     pc_request,
     pc_reset_agent_session,
+    pc_reset_case_agents,
     pc_respond_to_interaction,
     pc_restore_project,
     pc_wake_analyst_for_appraiser_facts,
@@ -4173,6 +4174,19 @@ async def api_post_interaction_response(
         raise HTTPException(502, f"שגיאת Paperclip: {e}")
 
 
+@app.post("/api/cases/{case_number}/agents/reset")
+async def api_reset_case_agents(case_number: str):
+    """Reset stuck agents for a case.
+
+    Clears writer/QA agents from 'error' status and reassigns any open
+    issues back to the chair user, stopping Paperclip recovery loops.
+    """
+    result = await pc_reset_case_agents(case_number)
+    if not result.get("ok"):
+        raise HTTPException(502, result.get("error", "שגיאה בביצוע האיפוס"))
+    return result
+
+
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