feat(email_gen): draft constituent letter generator + bill text indicators

- Add DraftLetterPanel: collapsible UI below BriefPanel for bills with a
  brief; lets users select up to 3 cited points, pick stance/tone, and
  generate a plain-text letter via the configured LLM provider
- Stance pre-fills from follow mode (pocket_boost → YES, pocket_veto → NO)
  and clears when the user unfollows; recipient derived from bill chamber
- Add POST /api/bills/{bill_id}/draft-letter endpoint with proper LLM
  provider/model resolution from AppSetting (respects Settings page choice)
- Add generate_text() to LLMProvider ABC and all four providers
- Expose has_document on BillSchema (list endpoint) via a single batch
  query; BillCard shows Brief / Pending / No text indicator per bill

Authored-By: Jack Levy

backend/app/api/bills.py

@@ -1,6 +1,7 @@
-from typing import Optional
+from typing import Literal, Optional
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, HTTPException, Query
+from pydantic import BaseModel
 from sqlalchemy import desc, func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
@@ -16,6 +17,30 @@ from app.schemas.schemas import (
     TrendScoreSchema,
 )
 
+_BILL_TYPE_LABELS: dict[str, str] = {
+    "hr": "H.R.",
+    "s": "S.",
+    "hjres": "H.J.Res.",
+    "sjres": "S.J.Res.",
+    "hconres": "H.Con.Res.",
+    "sconres": "S.Con.Res.",
+    "hres": "H.Res.",
+    "sres": "S.Res.",
+}
+
+
+class DraftLetterRequest(BaseModel):
+    stance: Literal["yes", "no"]
+    recipient: Literal["house", "senate"]
+    tone: Literal["short", "polite", "firm"]
+    selected_points: list[str]
+    include_citations: bool = True
+    zip_code: str | None = None  # not stored, not logged
+
+
+class DraftLetterResponse(BaseModel):
+    draft: str
+
 router = APIRouter()
 
 
@@ -67,7 +92,14 @@ async def list_bills(
     result = await db.execute(query)
     bills = result.scalars().unique().all()
 
-    # Attach latest brief and trend to each bill
+    # Single batch query: which of these bills have at least one document?
+    bill_ids = [b.bill_id for b in bills]
+    doc_result = await db.execute(
+        select(BillDocument.bill_id).where(BillDocument.bill_id.in_(bill_ids)).distinct()
+    )
+    bills_with_docs = {row[0] for row in doc_result}
+
+    # Attach latest brief, trend, and has_document to each bill
     items = []
     for bill in bills:
         bill_dict = BillSchema.model_validate(bill)
@@ -75,6 +107,7 @@ async def list_bills(
             bill_dict.latest_brief = bill.briefs[0]
         if bill.trend_scores:
             bill_dict.latest_trend = bill.trend_scores[0]
+        bill_dict.has_document = bill.bill_id in bills_with_docs
         items.append(bill_dict)
 
     return PaginatedResponse(
@@ -159,3 +192,50 @@ async def get_bill_trend(bill_id: str, days: int = Query(30, ge=7, le=365), db:
         .order_by(TrendScore.score_date)
     )
     return result.scalars().all()
+
+
+@router.post("/{bill_id}/draft-letter", response_model=DraftLetterResponse)
+async def generate_letter(bill_id: str, body: DraftLetterRequest, db: AsyncSession = Depends(get_db)):
+    from app.models.setting import AppSetting
+    from app.services.llm_service import generate_draft_letter
+
+    bill = await db.get(Bill, bill_id)
+    if not bill:
+        raise HTTPException(status_code=404, detail="Bill not found")
+
+    if not body.selected_points:
+        raise HTTPException(status_code=422, detail="At least one point must be selected")
+
+    prov_row = await db.get(AppSetting, "llm_provider")
+    model_row = await db.get(AppSetting, "llm_model")
+    llm_provider_override = prov_row.value if prov_row else None
+    llm_model_override = model_row.value if model_row else None
+
+    type_label = _BILL_TYPE_LABELS.get((bill.bill_type or "").lower(), (bill.bill_type or "").upper())
+    bill_label = f"{type_label} {bill.bill_number}"
+
+    try:
+        draft = generate_draft_letter(
+            bill_label=bill_label,
+            bill_title=bill.short_title or bill.title or bill_label,
+            stance=body.stance,
+            recipient=body.recipient,
+            tone=body.tone,
+            selected_points=body.selected_points,
+            include_citations=body.include_citations,
+            zip_code=body.zip_code,
+            llm_provider=llm_provider_override,
+            llm_model=llm_model_override,
+        )
+    except Exception as exc:
+        msg = str(exc)
+        if "insufficient_quota" in msg or "quota" in msg.lower():
+            detail = "LLM quota exceeded. Check your API key billing."
+        elif "rate_limit" in msg.lower() or "429" in msg:
+            detail = "LLM rate limit hit. Wait a moment and try again."
+        elif "auth" in msg.lower() or "401" in msg or "403" in msg:
+            detail = "LLM authentication failed. Check your API key."
+        else:
+            detail = f"LLM error: {msg[:200]}"
+        raise HTTPException(status_code=502, detail=detail)
+    return {"draft": draft}