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.

tests/unit/test_logs_tool.py

@@ -2,13 +2,26 @@
 from datetime import datetime
 from unittest.mock import patch
 
+import pytest
+
+from spark_executor.core import connection_store
 from spark_executor.core.job_store import JobStore
-from spark_executor.models import Job
+from spark_executor.models import Connection, Job
 from spark_executor.tools import logs
+from spark_executor.tools import connections
+
+
+def _fresh_stores():
+    store = connection_store.ConnectionStore()
+    connection_store.store = store
+    connections.store = store
+    logs.conn_store = store
+    logs.store = JobStore()
 
 
 def _seed(job_id="abc", app_id="application_1"):
-    logs.store = JobStore()
+    _fresh_stores()
+    logs.conn_store.save(Connection(name="prod", master="yarn", yarn_rm_url="http://rm:8088"))
     logs.store.put(
         Job(
             job_id=job_id,
@@ -43,6 +56,21 @@ def test_get_job_logs_respects_custom_tail_chars():
 
 def test_get_job_logs_raises_for_unknown_job():
     _seed()
-    import pytest
     with pytest.raises(KeyError):
         logs.get_job_logs("missing")
+
+
+def test_get_job_logs_raises_when_connection_missing():
+    _fresh_stores()
+    logs.store.put(
+        Job(
+            job_id="abc",
+            application_id="application_1",
+            script_path="/tmp/j.py",
+            queue="default",
+            submit_time=datetime(2026, 6, 24),
+            connection="missing",
+        )
+    )
+    with pytest.raises(KeyError, match="Connection not found"):
+        logs.get_job_logs("abc")