feat: port conflict validation, autosave on Apply, extended integration tests

Port conflict validation:
- api/port_registry.py: detect_conflicts() checks all service sections for shared port values
- api/app.py: returns HTTP 409 on port conflict after existing range validation
- webui/src/pages/Settings.jsx: JS-side detectPortConflicts() with useMemo shows inline
  conflict errors and blocks Save before the request is made; catch blocks surface server
  error messages (including 409) instead of generic fallbacks

Config autosave on Apply:
- webui/src/contexts/DraftConfigContext.jsx: new context; Settings registers flush callbacks
  per section; App calls flushAll() before applyPending() when any section is dirty
- webui/src/App.jsx: wraps tree with DraftConfigProvider, handleApply shows 'saving' banner
  state and awaits flushAll()
- webui/src/pages/Settings.jsx: registers identity + per-service flushers; propagates dirty
  state into context via setDirty; uses refs to avoid stale closures

Extended integration test coverage (114 new tests):
- tests/integration/test_config_api.py: GET/PUT config, export, import, backup lifecycle
- tests/integration/test_network_services.py: DNS records + DHCP reservations CRUD
- tests/integration/test_containers.py: list, restart, logs, stats; recovery polling
- tests/integration/test_negative_scenarios.py: error-path coverage for all endpoints
- tests/test_port_conflicts.py: 20 unit tests for port_registry.detect_conflicts()

Pre-commit hook updated to skip tests/integration/ (live-stack tests require a running
stack and must be run explicitly via `make test-integration`).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/port_registry.py

@@ -0,0 +1,67 @@
+"""
+Port conflict detection for PIC.
+
+Maps each service section to the port field names it exposes, and provides
+detect_conflicts() to find cases where two distinct (section, field) slots
+resolve to the same integer port value.
+"""
+
+# Maps section → list of port field names within that section's config dict.
+# Must stay in sync with the _port_fields dict in app.py's update_config().
+PORT_FIELDS = {
+    'network':   ['dns_port'],
+    'wireguard': ['port'],
+    'email':     ['smtp_port', 'submission_port', 'imap_port', 'webmail_port'],
+    'calendar':  ['port'],
+    'files':     ['port', 'manager_port'],
+}
+
+
+def detect_conflicts(effective_config, incoming_patch):
+    """
+    Detect port conflicts across all tracked service sections.
+
+    Parameters
+    ----------
+    effective_config : dict
+        The current full config as stored (e.g. config_manager.configs).
+        Each key is a section name; the value is a dict of that section's
+        config fields.
+    incoming_patch : dict
+        The partial update the user is trying to save.  Values here override
+        whatever is in effective_config for the purpose of conflict checking.
+
+    Returns
+    -------
+    list of dict
+        Each element is {'port': <int>, 'conflicts': [(section, field), ...]}.
+        Only entries where 2+ (section, field) pairs share the same port are
+        included.  Returns an empty list when there are no conflicts.
+    """
+    # Build merged view: start from stored config, overlay the patch
+    merged = {}
+    for section in PORT_FIELDS:
+        stored = effective_config.get(section, {}) or {}
+        patch = incoming_patch.get(section, {}) or {}
+        merged[section] = {**stored, **patch}
+
+    # Collect port → [(section, field)] mapping
+    port_map = {}
+    for section, fields in PORT_FIELDS.items():
+        for field in fields:
+            raw = merged[section].get(field)
+            if raw is None or raw == '':
+                continue
+            try:
+                port_val = int(raw)
+            except (ValueError, TypeError):
+                continue
+            port_map.setdefault(port_val, []).append((section, field))
+
+    # Return only entries that have more than one (section, field) slot
+    conflicts = []
+    for port_val, slots in port_map.items():
+        if len(slots) >= 2:
+            conflicts.append({'port': port_val, 'conflicts': slots})
+
+    return conflicts