Improve block-zayin: synthesize claims by topic + fix markdown JSON parsing

block_writer: Rewrote block-zayin prompt to require synthesis by topic
instead of listing each claim separately. Now produces 3 organized
sections (appellants 8, committee 6, permit applicants 3+) instead
of 40 scattered paragraphs. Target: 800-1500 words.

claims_extractor: Fix markdown code block stripping (same bug as
qa_validator had). Enables parsing claims from Claude responses
wrapped in ```json blocks.

Tested on Hecht: block-zayin from 40 paragraphs/1049 words to
17 organized paragraphs/1039 words. Structure now matches Dafna's
original (3 parties, grouped by topic).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/claims_extractor.py

@@ -105,6 +105,9 @@ async def extract_claims_with_ai(
     )
 
     raw = message.content[0].text.strip()
+    # Strip markdown code blocks if present
+    raw = re.sub(r"^```(?:json)?\s*", "", raw)
+    raw = re.sub(r"\s*```$", "", raw)
     try:
         # Extract JSON array from response
         json_match = re.search(r"\[.*\]", raw, re.DOTALL)