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>

shopdb/core/models/relationship.py

@@ -115,59 +115,3 @@ class AssetRelationship(BaseModel):
 
     def __repr__(self):
         return f"<AssetRelationship {self.sourceassetid} -> {self.targetassetid}>"
-
-
-class MachineRelationship(BaseModel):
-    """
-    Relationships between machines.
-
-    Examples:
-    - PC controls CNC machine
-    - Two CNCs are dualpath partners
-    """
-    __tablename__ = 'machinerelationships'
-
-    relationshipid = db.Column(db.Integer, primary_key=True)
-
-    parentmachineid = db.Column(
-        db.Integer,
-        db.ForeignKey('machines.machineid'),
-        nullable=False
-    )
-    childmachineid = db.Column(
-        db.Integer,
-        db.ForeignKey('machines.machineid'),
-        nullable=False
-    )
-    relationshiptypeid = db.Column(
-        db.Integer,
-        db.ForeignKey('relationshiptypes.relationshiptypeid'),
-        nullable=False
-    )
-
-    notes = db.Column(db.Text)
-
-    # Relationships
-    parent_machine = db.relationship(
-        'Machine',
-        foreign_keys=[parentmachineid],
-        backref='child_relationships'
-    )
-    child_machine = db.relationship(
-        'Machine',
-        foreign_keys=[childmachineid],
-        backref='parent_relationships'
-    )
-    relationship_type = db.relationship('RelationshipType', backref='relationships')
-
-    __table_args__ = (
-        db.UniqueConstraint(
-            'parentmachineid',
-            'childmachineid',
-            'relationshiptypeid',
-            name='uq_machine_relationship'
-        ),
-    )
-
-    def __repr__(self):
-        return f"<MachineRelationship {self.parentmachineid} -> {self.childmachineid}>"