feat(phase2): fact/inference labeling, change-driven alerts, admin cleanup

- Add label: cited_fact | inference to LLM brief schema (all 4 providers)
- Inferred badge in AIBriefCard for inference-labeled points
- backfill_brief_labels Celery task: classifies existing cited points in-place
- POST /api/admin/backfill-labels + unlabeled_briefs stat counter
- Expand milestone keywords: markup, conference
- Add is_referral_action() for committee referrals (referred to)
- Two-tier milestone notifications: progress tier (all follow modes) and
  referral tier (pocket_veto/boost only, neutral suppressed)
- Topic followers now receive bill_updated milestone notifications via
  latest brief topic_tags lookup in _update_bill_if_changed()
- Admin Manual Controls: collapsible Maintenance section for backfill tasks
- Update ARCHITECTURE.md and roadmap for Phase 2 completion

Co-Authored-By: Jack Levy

backend/app/services/llm_service.py

@@ -22,10 +22,10 @@ Always respond with valid JSON matching exactly this schema:
 {
   "summary": "2-4 paragraph plain-language summary of what this bill does",
   "key_points": [
-    {"text": "specific concrete fact", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words"}
+    {"text": "specific concrete fact", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words", "label": "cited_fact"}
   ],
   "risks": [
-    {"text": "legitimate concern or challenge", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words"}
+    {"text": "legitimate concern or challenge", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words", "label": "cited_fact"}
   ],
   "deadlines": [{"date": "YYYY-MM-DD or null", "description": "what happens on this date"}],
   "topic_tags": ["healthcare", "taxation"]
@@ -35,10 +35,14 @@ Rules:
 - summary: Explain WHAT the bill does, not whether it is good or bad. Be factual and complete.
 - key_points: 5-10 specific, concrete things the bill changes, authorizes, or appropriates. \
 Each item MUST include "text" (your claim), "citation" (the section number, e.g. "Section 301(a)(2)"), \
-and "quote" (a verbatim excerpt of ≤80 words from that section that supports your claim).
+"quote" (a verbatim excerpt of ≤80 words from that section that supports your claim), and "label".
 - risks: Legitimate concerns from any perspective — costs, implementation challenges, \
 constitutional questions, unintended consequences. Include at least 2 even for benign bills. \
-Each item MUST include "text", "citation", and "quote" just like key_points.
+Each item MUST include "text", "citation", "quote", and "label" just like key_points.
+- label: "cited_fact" if the claim is directly and explicitly stated in the quoted text. \
+"inference" if the claim is an analytical interpretation, projection, or implication that goes \
+beyond what the text literally says (e.g. projected costs, likely downstream effects, \
+constitutional questions). When in doubt, use "inference".
 - deadlines: Only include if explicitly stated in the text. Use null for date if a deadline \
 is mentioned without a specific date. Empty list if none.
 - topic_tags: 3-8 lowercase tags. Prefer these standard tags: healthcare, taxation, defense, \
@@ -90,10 +94,10 @@ Always respond with valid JSON matching exactly this schema:
 {
   "summary": "2-3 paragraph plain-language description of what changed in this version",
   "key_points": [
-    {"text": "specific change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words"}
+    {"text": "specific change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words", "label": "cited_fact"}
   ],
   "risks": [
-    {"text": "new concern introduced by this change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words"}
+    {"text": "new concern introduced by this change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words", "label": "cited_fact"}
   ],
   "deadlines": [{"date": "YYYY-MM-DD or null", "description": "new deadline added"}],
   "topic_tags": ["healthcare", "taxation"]
@@ -103,9 +107,12 @@ Rules:
 - summary: Focus ONLY on what is different from the previous version. Be specific.
 - key_points: List concrete additions, removals, or modifications in this version. \
 Each item MUST include "text" (your claim), "citation" (the section number, e.g. "Section 301(a)(2)"), \
-and "quote" (a verbatim excerpt of ≤80 words from the NEW version that supports your claim).
+"quote" (a verbatim excerpt of ≤80 words from the NEW version that supports your claim), and "label".
 - risks: Only include risks that are new or changed relative to the previous version. \
-Each item MUST include "text", "citation", and "quote" just like key_points.
+Each item MUST include "text", "citation", "quote", and "label" just like key_points.
+- label: "cited_fact" if the claim is directly and explicitly stated in the quoted text. \
+"inference" if the claim is an analytical interpretation, projection, or implication that goes \
+beyond what the text literally says. When in doubt, use "inference".
 - deadlines: Only new or changed deadlines. Empty list if none.
 - topic_tags: Same standard tags as before — include any new topics this version adds.