feat: cleanup phase and main service loop with error isolation

Wires capture -> apply -> cleanup into cycle(cfg): per-file capture and
cleanup each wrapped in try/except + log.exception so one file's failure
does not abort the cycle; apply failure does not block cleanup; writer is
always closed in finally. run(cfg) loops cycle with sleep; main() loads
config from argv. logging_setup uses RotatingFileHandler 10MBx5 + console.

Unit tests cover all three error-isolation branches via mocks (no real
end-to-end smoke; integration deferred to Task 9 pilot).

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

src/sync/logging_setup.py

@@ -0,0 +1,30 @@
+"""Logging configuration for the sync service.
+
+Configures the root logger with a RotatingFileHandler (10 MB x 5, UTF-8) plus
+a console StreamHandler. The level and log path come from ``cfg.logging``.
+"""
+import logging
+import logging.handlers
+import os
+
+
+def setup_logging(cfg_dict: dict | None):
+    """Configure root logging from the ``cfg.logging`` dict.
+
+    ``cfg_dict`` is ``SyncConfig.logging`` (a dict or None). ``level`` is a
+    logging-level name string (default ``"INFO"``); ``path`` is the log file
+    path (default ``"sync.log"``). The parent directory is created if missing.
+    """
+    level = getattr(logging, (cfg_dict or {}).get("level", "INFO")) if cfg_dict else logging.INFO
+    path = (cfg_dict or {}).get("path", "sync.log")
+    os.makedirs(os.path.dirname(path) or ".", exist_ok=True)
+    h = logging.handlers.RotatingFileHandler(
+        path, maxBytes=10 * 1024 * 1024, backupCount=5, encoding="utf-8"
+    )
+    h.setFormatter(logging.Formatter("%(asctime)s %(levelname)s [%(name)s] %(message)s"))
+    root = logging.getLogger()
+    root.setLevel(level)
+    root.addHandler(h)
+    sh = logging.StreamHandler()
+    sh.setFormatter(logging.Formatter("%(levelname)s %(message)s"))
+    root.addHandler(sh)