feat(citations): add per-claim citations to AI briefs

LLM prompts updated to output {text, citation, quote} objects for every
key_point and risk. govinfo_url stored on BillBrief (migration 0006) so
the frontend can link directly to the source document without an extra
query. AIBriefCard renders § citation chips that expand inline to show
the verbatim quote and a View source → GovInfo link. Old plain-string
briefs continue to render unchanged.

Authored-By: Jack Levy

backend/app/services/llm_service.py

@@ -21,17 +21,24 @@ without political bias.
 Always respond with valid JSON matching exactly this schema:
 {
   "summary": "2-4 paragraph plain-language summary of what this bill does",
-  "key_points": ["specific concrete fact 1", "specific concrete fact 2"],
-  "risks": ["legitimate concern or challenge 1", "legitimate concern 2"],
+  "key_points": [
+    {"text": "specific concrete fact", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words"}
+  ],
+  "risks": [
+    {"text": "legitimate concern or challenge", "citation": "Section X(y)", "quote": "verbatim excerpt from bill ≤80 words"}
+  ],
   "deadlines": [{"date": "YYYY-MM-DD or null", "description": "what happens on this date"}],
   "topic_tags": ["healthcare", "taxation"]
 }
 
 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.
+- 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).
 - risks: Legitimate concerns from any perspective — costs, implementation challenges, \
-constitutional questions, unintended consequences. Include at least 2 even for benign bills.
+constitutional questions, unintended consequences. Include at least 2 even for benign bills. \
+Each item MUST include "text", "citation", and "quote" just like key_points.
 - 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, \
@@ -49,8 +56,8 @@ TOKENS_PER_CHAR = 0.25  # rough approximation: 4 chars ≈ 1 token
 @dataclass
 class ReverseBrief:
     summary: str
-    key_points: list[str]
-    risks: list[str]
+    key_points: list[dict]
+    risks: list[dict]
     deadlines: list[dict]
     topic_tags: list[str]
     llm_provider: str
@@ -82,16 +89,23 @@ and you must summarize what changed between the previous and new version.
 Always respond with valid JSON matching exactly this schema:
 {
   "summary": "2-3 paragraph plain-language description of what changed in this version",
-  "key_points": ["specific change 1", "specific change 2"],
-  "risks": ["new concern introduced by this change 1", "concern 2"],
+  "key_points": [
+    {"text": "specific change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words"}
+  ],
+  "risks": [
+    {"text": "new concern introduced by this change", "citation": "Section X(y)", "quote": "verbatim excerpt from new version ≤80 words"}
+  ],
   "deadlines": [{"date": "YYYY-MM-DD or null", "description": "new deadline added"}],
   "topic_tags": ["healthcare", "taxation"]
 }
 
 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.
-- risks: Only include risks that are new or changed relative to the previous version.
+- 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).
+- 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.
 - deadlines: Only new or changed deadlines. Empty list if none.
 - topic_tags: Same standard tags as before — include any new topics this version adds.