fix: apply all PR review agent findings (silent failures, type safety, test gaps)

Addresses issues found by 4 parallel review agents (code-reviewer,
silent-failure-hunter, type-design-analyzer, pr-test-analyzer).

Source fixes:
- core/utils.py: add public safe_display_url() (moved from tools/health.py)
- core/client.py: rename _redact_sensitive → redact_sensitive (public API)
- core/types.py: add SubscriptionData.__post_init__ for tz-aware datetime
  enforcement; remove 6 unused type aliases (SystemHealth, APIResponse, etc.)
- subscriptions/manager.py: add exc_info=True to both except-Exception blocks;
  add except ValueError break-on-config-error before retry loop; import
  redact_sensitive by new public name
- subscriptions/resources.py: re-raise in autostart_subscriptions() so
  ensure_subscriptions_started() doesn't permanently set _subscriptions_started
- subscriptions/diagnostics.py: except ToolError: raise before broad except;
  use safe_display_url() instead of raw URL slice
- tools/health.py: move _safe_display_url to core/utils; add exc_info=True;
  raise ToolError (not return dict) on ImportError
- tools/info.py: use get_args(INFO_ACTIONS) instead of INFO_ACTIONS.__args__
- tools/{array,docker,keys,notifications,rclone,storage,virtualization}.py:
  add Literal-vs-ALL_ACTIONS sync check at import time

Test fixes:
- test_health.py: import safe_display_url from core.utils; update
  test_diagnose_import_error_internal to expect ToolError (not error dict)
- test_storage.py: add 3 safe_get tests for zero/False/empty-string values
- test_subscription_manager.py: add TestCapLogContentSingleMassiveLine (2 tests)
- test_client.py: rename _redact_sensitive → redact_sensitive; add tests for
  new sensitive keys and is_cacheable explicit-keyword form

tests/test_storage.py

@@ -149,6 +149,15 @@ class TestSafeGet:
         result = safe_get({}, "missing", default=[])
         assert result == []
 
+    def test_zero_value_not_replaced_by_default(self) -> None:
+        assert safe_get({"temp": 0}, "temp", default="N/A") == 0
+
+    def test_false_value_not_replaced_by_default(self) -> None:
+        assert safe_get({"active": False}, "active", default=True) is False
+
+    def test_empty_string_not_replaced_by_default(self) -> None:
+        assert safe_get({"name": ""}, "name", default="unknown") == ""
+
 
 class TestStorageActions:
     async def test_shares(self, _mock_graphql: AsyncMock) -> None: