Add gauge lab + maintenance asset references with enable/disable toggles

Dedicated assets.gaugelabreference and assets.maintenancereference columns
(distinct from assetnumber), surfaced on equipment. Add global per-identifier
enable/disable settings (gauge/maintenance/FQDN) read via a shared composable
and toggled in System Settings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

migrations/versions/7b02_gaugelabreference.py

@@ -0,0 +1,44 @@
+"""Add Asset.gaugelabreference and Asset.maintenancereference
+
+Adds dedicated external-reference columns to assets, distinct from
+assetnumber. Equipment commonly carries an authoritative gauge lab reference
+and a maintenance system reference; assetnumber stays the generic asset tag
+and name the layperson label.
+
+Revision ID: 7b02_gaugelabref
+Revises: 7a01_adr001_position
+Create Date: 2026-06-25
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = '7b02_gaugelabref'
+down_revision = '7a01_adr001_position'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table('assets') as batch_op:
+        batch_op.add_column(sa.Column(
+            'gaugelabreference', sa.String(length=50), nullable=True,
+            comment='Gauge lab asset reference (authoritative tag the gauge '
+                    'lab assigns to equipment); distinct from assetnumber'))
+        batch_op.add_column(sa.Column(
+            'maintenancereference', sa.String(length=50), nullable=True,
+            comment='Maintenance system asset reference; distinct from '
+                    'assetnumber'))
+        batch_op.create_index('ix_assets_gaugelabreference',
+                              ['gaugelabreference'])
+        batch_op.create_index('ix_assets_maintenancereference',
+                              ['maintenancereference'])
+
+
+def downgrade():
+    with op.batch_alter_table('assets') as batch_op:
+        batch_op.drop_index('ix_assets_maintenancereference')
+        batch_op.drop_index('ix_assets_gaugelabreference')
+        batch_op.drop_column('maintenancereference')
+        batch_op.drop_column('gaugelabreference')