fix: logging verbosity now actually applies + per-service log levels

Root causes fixed:
- Dead LOG_LEVEL globals() lookup pinned root logger at INFO regardless of
  PIC_LOG_LEVEL env or config; replaced with _resolve_root_log_level() +
  apply_root_log_level() which sets both root logger and all attached handlers
  at startup and on runtime re-apply.
- set_service_level() only set the named 'pic.<service>' logger; bare module
  loggers (e.g. 'caddy_manager') were never reached, so per-service log files
  stayed 0 bytes. Fixed via _SERVICE_MODULE_LOGGERS map covering all managers.
- Log viewer GET /api/logs had no level filter; added ?level= query param.
- Per-service log levels lived in an out-of-band config/api/log_levels.json
  side-file with no validation; migrated into ConfigManager under a new
  'logging' section ({python:{root,services}, containers:{caddy,coredns,
  wireguard,mailserver,api}}) with get/set helpers, invalid-level rejection,
  and one-time migration from the old file on first load.

New capabilities:
- Container log levels: Caddy (injects global log { level X } + hot reload),
  CoreDNS (DEBUG enables log plugin, else errors-only), WireGuard/mailserver
  via pending_restart path.
- PUT /api/logs/verbosity accepts {python, containers} dict; returns per-entry
  applied:hot|pending_restart status.
- Webui Logs page gains two-section Verbosity tab (Python services + Container
  services) with needs-restart badges.
- managers.py wires per-service loggers before manager instantiation and
  re-applies persisted levels from ConfigManager; legacy log_levels.json read
  removed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_cell_link_dns.py

@@ -61,8 +61,17 @@ class TestGenerateCorefileOneLink(unittest.TestCase):
         self.assertIn('cache', content[idx_primary:])
 
     def test_log_directive_present_in_forwarding_block(self):
+        # At default INFO the forwarding block carries the `errors` directive;
+        # at DEBUG it carries the verbose `log` plugin.
         cell_links = [{'domain': 'remote.cell', 'dns_ip': '10.5.0.1'}]
-        firewall_manager.generate_corefile([], self.path, cell_links=cell_links)
+        firewall_manager.generate_corefile([], self.path, cell_links=cell_links,
+                                           coredns_level='INFO')
+        content = self._read()
+        idx_primary = content.index('remote.cell {')
+        self.assertIn('errors', content[idx_primary:])
+
+        firewall_manager.generate_corefile([], self.path, cell_links=cell_links,
+                                           coredns_level='DEBUG')
         content = self._read()
         idx_primary = content.index('remote.cell {')
         self.assertIn('log', content[idx_primary:])