feat(agents): mirror Paperclip interactions in case page

Surface issue_thread_interactions (ask_user_questions / request_confirmation /
suggest_tasks) directly inside legal-ai's case detail feed so the user can
answer agent prompts without switching to Paperclip's UI.

Backend (FastAPI):
- paperclip_client.py: 4 new helpers — get_issue_interactions (DB),
  respond_to_interaction / accept_interaction / reject_interaction (REST).
- app.py: extends GET /api/cases/{case_number}/agents to include
  `interactions`, and adds POST /api/cases/{case_number}/agents/interaction-response
  routing to /respond, /accept, /reject in Paperclip.
- paperclip_client.py: also pulls existing httpx calls onto the centralized
  pc_request helper (paperclip_api.py) for consistent auth + run-id headers.

Frontend (web-ui, Next.js 16 + TanStack Query):
- agents.ts: Interaction / InteractionPayload / InteractionStatus types,
  useSubmitInteraction mutation hook (invalidates the activity query).
- agent-activity-feed.tsx: InteractionCard renders radio (single) /
  checkbox (multi) for ask_user_questions, accept/reject + reason for
  request_confirmation, task selection for suggest_tasks. Resolved
  interactions show a read-only summary. Cards are interleaved with
  comments by created_at, so the feed reads chronologically.

Paperclip auto-wakes the issue assignee on a successful response
(queueResolvedInteractionContinuationWakeup) — no explicit wakeup needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/paperclip_api.py

@@ -0,0 +1,83 @@
+"""Paperclip REST API helper.
+
+All HTTP calls from legal-ai backend (FastAPI) to Paperclip should go through
+``pc_request`` so that auth + audit headers are applied consistently.
+
+The bash counterpart for agents lives at ``scripts/pc.sh``.
+
+Notes
+-----
+* Uses ``PAPERCLIP_BOARD_API_KEY`` (long-lived) — these are *board* actions
+  (wakeups, comments-as-user) initiated from outside a heartbeat, not agent
+  actions. Board API keys are not JWTs, so they do **not** carry a ``run_id``
+  claim; pass ``run_id=`` explicitly when you have one (rare for board flows).
+* For agent actions inside a heartbeat run, agents use the bash helper with
+  the auto-injected ``PAPERCLIP_API_KEY`` JWT — those carry ``run_id`` in
+  claims, so the header is informational/future-proofing.
+"""
+from __future__ import annotations
+
+import logging
+import os
+from typing import Any
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+PAPERCLIP_API_URL = os.environ.get("PAPERCLIP_API_URL", "http://localhost:3100")
+PAPERCLIP_BOARD_API_KEY = os.environ.get("PAPERCLIP_BOARD_API_KEY", "")
+
+DEFAULT_TIMEOUT = 15.0
+
+
+def _build_headers(run_id: str | None, has_body: bool) -> dict[str, str]:
+    if not PAPERCLIP_BOARD_API_KEY:
+        raise RuntimeError("PAPERCLIP_BOARD_API_KEY not set — cannot call Paperclip API")
+    headers = {
+        "Authorization": f"Bearer {PAPERCLIP_BOARD_API_KEY}",
+        "X-Paperclip-Run-Id": run_id or "",
+    }
+    if has_body:
+        headers["Content-Type"] = "application/json"
+    return headers
+
+
+async def pc_request(
+    method: str,
+    path: str,
+    *,
+    json: dict[str, Any] | None = None,
+    run_id: str | None = None,
+    timeout: float = DEFAULT_TIMEOUT,
+    raise_on_error: bool = False,
+) -> httpx.Response:
+    """Make a Paperclip REST request.
+
+    Parameters
+    ----------
+    method : str
+        HTTP method (GET, POST, PATCH, DELETE).
+    path : str
+        Path relative to PAPERCLIP_API_URL (must start with ``/``).
+    json : dict, optional
+        Request body — sent as JSON.
+    run_id : str, optional
+        Heartbeat run ID for audit trail (X-Paperclip-Run-Id header).
+        Rare for board actions; provide when initiating from inside a run.
+    timeout : float
+        httpx timeout (default 15s).
+    raise_on_error : bool
+        If True, calls ``response.raise_for_status()`` on 4xx/5xx.
+
+    Returns
+    -------
+    httpx.Response
+    """
+    headers = _build_headers(run_id, has_body=json is not None)
+    url = f"{PAPERCLIP_API_URL}{path}"
+    async with httpx.AsyncClient(timeout=timeout) as client:
+        resp = await client.request(method, url, headers=headers, json=json)
+    if raise_on_error:
+        resp.raise_for_status()
+    return resp