Add business spans and silence the frontend health poll

Manual INTERNAL spans for the business steps the auto-instrumentation
can't name: fraud.score_transaction, sanctions.lookup_watchlist,
ledger.settle and insights.aggregate_120d, with ledgerline.* attributes
(account, amount, risk score, match outcome). holder_name stays off the
spans. Each span starts after its handler's chaos flag reads and
injection points, and no chaos-derived values become attributes.

The gateway's /api/health/all fan-out now runs under
suppress_instrumentation: with the route excluded, its five downstream
/healthz calls were each a parentless root trace.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/ledger/app.py

@@ -1,6 +1,7 @@
 from fastapi import FastAPI, Request
 from fastapi.responses import JSONResponse
 from pydantic import BaseModel, field_validator
+from opentelemetry import trace
 from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
 from opentelemetry.instrumentation.sqlalchemy import SQLAlchemyInstrumentor
 
@@ -13,6 +14,7 @@ from . import repository
 
 SERVICE_NAME = "ledger"
 logger = configure_logging(SERVICE_NAME)
+tracer = trace.get_tracer(__name__)
 setup_telemetry(service_name=SERVICE_NAME)
 app = FastAPI(title=SERVICE_NAME)
 
@@ -133,13 +135,19 @@ async def settle(tx_id: str, body: SettleRequest):
     starved = await chaos.pool_starvation_enabled()
     row_lock = await chaos.row_lock_contention_enabled()
 
-    async with session_factory(starved=starved) as session:
-        tx = await repository.get_transaction(session, tx_id)
-        if tx is None:
-            return JSONResponse(status_code=404, content={"error": "transaction not found"})
-        account = await repository.get_account(session, tx.account_id)
-        use_lock = row_lock and bool(account.is_hot)
-        balance = await repository.settle_transaction(session, tx=tx, risk_score=body.risk_score, use_row_lock=use_lock)
+    with tracer.start_as_current_span(
+        "ledger.settle",
+        attributes={"ledgerline.tx.id": tx_id, "ledgerline.risk.score": body.risk_score},
+    ) as span:
+        async with session_factory(starved=starved) as session:
+            tx = await repository.get_transaction(session, tx_id)
+            if tx is None:
+                return JSONResponse(status_code=404, content={"error": "transaction not found"})
+            span.set_attribute("ledgerline.account.id", str(tx.account_id))
+            span.set_attribute("ledgerline.tx.amount_minor", tx.amount_minor)
+            account = await repository.get_account(session, tx.account_id)
+            use_lock = row_lock and bool(account.is_hot)
+            balance = await repository.settle_transaction(session, tx=tx, risk_score=body.risk_score, use_row_lock=use_lock)
 
     logger.info(f"settled transaction {tx_id} request_id={body.request_id}")
     return {"status": "settled", "balance_minor": balance}