Add --debug flag, dual-mode logging, and auto-run on startup

- logger.py: root-level handlers; normal mode shows only user-facing INFO
  (sync, export, push, MBOX) plus WARNING/ERROR; --debug shows all DEBUG
  with full context (module.func:line). Third-party loggers silenced to WARNING.
- main.py: add --debug CLI flag, call configure_logging() at startup,
  auto-trigger sync on first run or when last sync is overdue by the interval
- database.py: add metadata table with record_sync_time() / get_last_sync_time()
  so startup knows whether a sync is due; sync time recorded on success
- forwarder.py: INFO at push start and push complete with counts
- packager.py: INFO before MBOX conversion begins
- exporter.py: INFO when Proton Mail export starts

https://claude.ai/code/session_01KjaNo9RXevw6x1DjJD8mj6

modules/forwarder.py

@@ -47,6 +47,8 @@ def push_emails(
     if not emails:
         return [], []
 
+    log.info("Starting IMAP push of %d email(s) to iCloud...", len(emails))
+
     succeeded: list[str] = []
     failed: list[str] = []
 
@@ -70,8 +72,11 @@ def push_emails(
 
     if succeeded:
         mark_delivered(succeeded)
-        log.info("Marked %d message(s) as delivered.", len(succeeded))
 
+    log.info(
+        "IMAP push complete — %d delivered, %d failed.",
+        len(succeeded), len(failed),
+    )
     return succeeded, failed