feat(settings): add Blocks tab — 12-block decision schema reference

Read-only display of BLOCK_CONFIG from block_writer.py with CREAC role
and JWM functional-purpose annotations per block (sourced from
docs/block-schema.md).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/app.py

@@ -2830,6 +2830,53 @@ async def api_mcp_registrations():
     return list_registrations()
 
 
+@app.get("/api/settings/mcp/blocks")
+async def api_mcp_blocks():
+    """List the 12-block decision schema (read-only reference)."""
+    from legal_mcp.services.block_writer import BLOCK_CONFIG
+
+    # CREAC role per block (from docs/block-schema.md). Static map —
+    # kept here rather than in BLOCK_CONFIG to avoid coupling LLM
+    # generation config to documentation metadata.
+    CREAC_ROLE = {
+        "block-alef": None, "block-bet": None, "block-gimel": None,
+        "block-dalet": None, "block-yod-bet": None,
+        "block-he": "Conclusion (preview)",
+        "block-vav": "Facts (R-context)",
+        "block-zayin": "Arguments",
+        "block-chet": "Procedural record",
+        "block-tet": "Rule (R)",
+        "block-yod": "C → R → E → A → C (full CREAC)",
+        "block-yod-alef": "Conclusion (final)",
+    }
+    # JWM functional purpose (Federal Judicial Center mapping)
+    JWM_PURPOSE = {
+        "block-alef": "Orientation", "block-bet": "Orientation",
+        "block-gimel": "Orientation", "block-dalet": "Orientation",
+        "block-he": "Orientation",
+        "block-vav": "Framing", "block-zayin": "Argumentation",
+        "block-chet": "Procedural record",
+        "block-tet": "Deliberation (rules)",
+        "block-yod": "Deliberation (analysis)",
+        "block-yod-alef": "Disposition",
+        "block-yod-bet": "Disposition (signatures)",
+    }
+    blocks = []
+    for block_id, cfg in sorted(BLOCK_CONFIG.items(), key=lambda kv: kv[1]["index"]):
+        blocks.append({
+            "id": block_id,
+            "index": cfg["index"],
+            "title": cfg["title"],
+            "gen_type": cfg["gen_type"],
+            "model": cfg["model"],
+            "temperature": cfg.get("temp"),
+            "max_tokens": cfg.get("max_tokens"),
+            "creac_role": CREAC_ROLE.get(block_id),
+            "jwm_purpose": JWM_PURPOSE.get(block_id),
+        })
+    return {"blocks": blocks, "count": len(blocks)}
+
+
 # ── Settings: Tag → Company Mappings ──────────────────────────────
 
 @app.get("/api/settings/paperclip-companies")