fix: migration 004 — force enable logs and services modules

INSERT OR IGNORE in migration 003 was silently skipped because
logs/services rows already existed in the DB with is_enabled=0.
Migration 004 uses ON CONFLICT DO UPDATE to ensure is_enabled=1.

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

backend/internal/db/migrations/004_enable_modules.sql

@@ -0,0 +1,6 @@
+-- Migration 004 : Activation des modules logs et services
+-- Les entrées peuvent exister avec is_enabled=0 (INSERT OR IGNORE de la 003 ignoré)
+INSERT INTO modules (id, name, description, version, is_core, is_enabled) VALUES
+    ('logs',     'Journaux',  'Consultation des journaux système via journalctl',   '1.0.0', 0, 1),
+    ('services', 'Services',  'Gestion des services systemd (start/stop/restart)', '1.0.0', 0, 1)
+ON CONFLICT(id) DO UPDATE SET is_enabled = 1;