Add service information feature with version checks

This commit introduces a new "Service Information" section displaying runtime details, installed version, and update status for the NexaPG application. It includes backend API endpoints, database schema changes, and a corresponding frontend page that allows users to check for updates against the official repository. The `.env` example now includes an `APP_VERSION` variable, and related documentation has been updated.

backend/alembic/versions/0008_service_settings.py

@@ -0,0 +1,34 @@
+"""add service info settings
+
+Revision ID: 0008_service_settings
+Revises: 0007_email_templates
+Create Date: 2026-02-13
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0008_service_settings"
+down_revision = "0007_email_templates"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "service_info_settings",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("current_version", sa.String(length=64), nullable=False, server_default="0.1.0"),
+        sa.Column("release_check_url", sa.String(length=500), nullable=True),
+        sa.Column("latest_version", sa.String(length=64), nullable=True),
+        sa.Column("update_available", sa.Boolean(), nullable=False, server_default=sa.false()),
+        sa.Column("last_checked_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("last_check_error", sa.Text(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.text("now()")),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("service_info_settings")