feat(yarn_client): SSL/TLS config for YARN REST connections

Add per-Connection ssl_verify / ssl_ca_bundle plus global defaults so
CDH 5 / on-prem clusters with self-signed certs or custom CA bundles can
be queried without patching code.

- Connection gets ssl_verify (bool|None) and ssl_ca_bundle (str|None)
- Settings gets ssl_verify_default and ssl_ca_bundle_default
- New YarnClientConfig dataclass carries the resolved verify= value
- _request passes verify= through to httpx.request
- All public yarn_client functions now take YarnClientConfig instead of
  a bare yarn_rm_url string; tool call sites resolve the Connection
- SaveConnectionRequest exposes the two new fields

Tests cover per-connection CA bundle, per-connection verify=False,
global default fallback, and connection-not-found error.

spark_executor/tools/result.py

@@ -7,7 +7,8 @@ import json
 
 from common.logging import logger
 from spark_executor.core.job_store import JobStore
-from spark_executor.core.yarn_client import get_application_status
+from spark_executor.core.yarn_client import YarnClientConfig, get_application_status
+from spark_executor.tools.connections import store as conn_store
 from spark_executor.models import JobResult
 
 store = JobStore()
@@ -18,7 +19,11 @@ def get_job_result(job_id: str) -> JobResult:
     job = store.get(job_id)
     if job is None:
         raise KeyError(f"Unknown job_id: {job_id}")
-    state, raw = get_application_status(job.application_id, job.yarn_rm_url)
+    conn = conn_store.get(job.connection)
+    if conn is None:
+        raise KeyError(f"Connection not found: {job.connection}")
+    config = YarnClientConfig.from_connection(conn)
+    state, raw = get_application_status(job.application_id, config)
     app = json.loads(raw).get("app", {})
     result = JobResult(
         application_id=job.application_id,