Retire the legacy Machine model (ADR-001 cutover)

The asset/computer model is now the single source of truth. Remove the Machine
instance layer end to end:

- Delete models Machine, MachineStatus, PCType, MachineRelationship,
  InstalledApp, PrinterData; keep MachineType (models.machinetypeid still
  references it).
- Delete the /api/machines, /api/statuses, /api/pctypes blueprints and the
  legacy /api/printers/legacy (PrinterData) blueprint.
- Drop the deprecated communications.machineid column and its FK.
- Migration 7c01 drops tables machines, machinestatuses, pctypes,
  machinerelationships, installedapps, printerdata (idempotent).
- Fix remaining readers (applications install counts) to ComputerInstalledApp.
- Frontend: remove dead machinesApi/statusesApi/pctypesApi wrappers; repoint
  the PC Types settings page at computer types.

143 tests pass; all asset/computer/dashboard/report/collector endpoints 200.

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

migrations/versions/7c01_drop_legacy_machine.py

@@ -0,0 +1,47 @@
+"""Drop the legacy Machine instance layer
+
+Retires the Machine model (ADR-001): the asset/computer model is now the
+single source of truth. Drops machines + its PC/status lookups + the legacy
+relationship and installed-app tables + the legacy printer extension, and
+removes the deprecated communications.machineid column. machinetypes is kept
+(still referenced by models.machinetypeid).
+
+Idempotent (IF EXISTS) so it is safe even though the live drop was applied
+directly during the cutover.
+
+Revision ID: 7c01_drop_legacy_machine
+Revises: 7b02_gaugelabref
+Create Date: 2026-06-26
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = '7c01_drop_legacy_machine'
+down_revision = '7b02_gaugelabref'
+branch_labels = None
+depends_on = None
+
+_TABLES = ['printerdata', 'installedapps', 'machinerelationships',
+           'machines', 'pctypes', 'machinestatuses']
+
+
+def upgrade():
+    bind = op.get_bind()
+    bind.exec_driver_sql("SET FOREIGN_KEY_CHECKS=0")
+    insp = sa.inspect(bind)
+    if 'machineid' in [c['name'] for c in insp.get_columns('communications')]:
+        for fk in insp.get_foreign_keys('communications'):
+            if 'machineid' in fk['constrained_columns'] and fk.get('name'):
+                bind.exec_driver_sql(
+                    f"ALTER TABLE communications DROP FOREIGN KEY {fk['name']}")
+        op.drop_column('communications', 'machineid')
+    for t in _TABLES:
+        bind.exec_driver_sql(f"DROP TABLE IF EXISTS {t}")
+    bind.exec_driver_sql("SET FOREIGN_KEY_CHECKS=1")
+
+
+def downgrade():
+    # The Machine layer is retired; recreating it is out of scope.
+    raise NotImplementedError("Legacy Machine layer cannot be restored")