refactor(src): Phase 10.2 batch 5 - log_registry + models + multi_agent_conductor + theme_2

For these 4 sites, the Result migration cascades badly (the function
returns a non-Result type that's used in many places). Per the audit's
heuristic #19 (catch + log = INTERNAL_COMPLIANT), we convert the
SILENT_SWALLOW to narrow-catch + sys.stderr.write. This satisfies the
no-silent-recovery principle while keeping the public API stable.

log_registry.py:249 (2 sites - inner + outer try/except for OSError
on session path scan and comms.log read)

models.py:508 (datetime.fromisoformat ValueError; field stays as
string on parse failure; logs the parse error to stderr)

multi_agent_conductor.py:317 (PersonaManager.load_all fallback for
ticket.persona_id lookup; logs the failure to stderr)

theme_2.py:282 (markdown_helper.get_renderer().clear_cache; logs
the import/attribute error to stderr)

Tests verified:
- tests/test_log_registry.py (5 tests) PASS
- tests/test_logging_e2e.py (1 test) PASS
- tests/test_auto_whitelist.py (4 tests) PASS
- tests/test_orchestration_logic.py (8 tests) PASS
- tests/test_mma_tier_usage_reset_fix.py (4 tests) PASS

src/log_registry.py

@@ -244,10 +244,12 @@ class LogRegistry:
          for kw in keywords_to_check:
           if kw in line and kw not in found_keywords:
            found_keywords.append(kw)
-      except OSError:
-       pass
-  except OSError:
-   pass
+      except OSError as e:
+       import sys
+       sys.stderr.write(f"[LogRegistry] read comms.log entry failed: {e}\n")
+  except OSError as e:
+   import sys
+   sys.stderr.write(f"[LogRegistry] scan session_path failed: {e}\n")
   size_kb     = total_size_bytes / 1024
   whitelisted = False
   reason      = ""