Add formboard harness layout designer

Separate read-only canvas for physically laying out wire harnesses.
Syncs connectors from the main diagram (one-way), no changes flow back.

Backend:
- FormboardLayout, FormboardNode, FormboardSegment models
- /api/formboard/ router: get/create layout, sync connectors from diagram,
  full CRUD for nodes and segments

Frontend (formboard.js):
- Konva canvas: drag nodes, click-to-connect segments, zoom/pan
- Node types: Connector (blue rect, synced from diagram), Branch (green
  circle, manual), Splice/joint (orange diamond, manual)
- Segments scale thickness by wire count; fitting overlays for open,
  split loom, conduit, heat shrink, tape wrap
- Right-click context menu for delete on nodes/segments

App integration:
- "⊞ Formboard" tab in view-tab-bar (distinct color, independent of views)
- Sub-toolbar: Select / Branch / Splice / Connect / Sync / Fit / Delete
- Right panel swaps to formboard props when active:
  - Node: label, notes, linked device info
  - Segment: fitting type, fitting color, label, length, wire checklist
    (checkboxes for every wire in the main diagram)

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

backend/app/models.py

@@ -124,6 +124,45 @@ class ViewWireWaypoints(Base):
     view = relationship("DiagramView", back_populates="wire_waypoints")
 
 
+class FormboardLayout(Base):
+    __tablename__ = "formboard_layouts"
+    id         = Column(Integer, primary_key=True, index=True)
+    diagram_id = Column(Integer, ForeignKey("diagrams.id", ondelete="CASCADE"), nullable=False, unique=True)
+
+    nodes    = relationship("FormboardNode",    back_populates="layout", cascade="all, delete-orphan")
+    segments = relationship("FormboardSegment", back_populates="layout", cascade="all, delete-orphan")
+
+
+class FormboardNode(Base):
+    __tablename__ = "formboard_nodes"
+    id        = Column(Integer, primary_key=True, index=True)
+    layout_id = Column(Integer, ForeignKey("formboard_layouts.id", ondelete="CASCADE"), nullable=False)
+    node_type = Column(String,  default="branch")   # connector | branch | splice
+    device_id = Column(Integer, ForeignKey("devices.id", ondelete="SET NULL"), nullable=True)
+    x         = Column(Float,   default=100)
+    y         = Column(Float,   default=100)
+    label     = Column(String,  default="")
+    notes     = Column(Text,    default="")
+
+    layout = relationship("FormboardLayout", back_populates="nodes")
+
+
+class FormboardSegment(Base):
+    __tablename__ = "formboard_segments"
+    id           = Column(Integer, primary_key=True, index=True)
+    layout_id    = Column(Integer, ForeignKey("formboard_layouts.id", ondelete="CASCADE"), nullable=False)
+    from_node_id = Column(Integer, ForeignKey("formboard_nodes.id",   ondelete="CASCADE"), nullable=False)
+    to_node_id   = Column(Integer, ForeignKey("formboard_nodes.id",   ondelete="CASCADE"), nullable=False)
+    waypoints    = Column(JSON,    default=[])
+    wire_ids     = Column(JSON,    default=[])       # wire IDs from main diagram
+    fitting_type = Column(String,  default="open")   # open | loom | conduit | heat_shrink | tape
+    fitting_color = Column(String, default="#888888")
+    label        = Column(String,  default="")
+    length_mm    = Column(Float,   nullable=True)
+
+    layout = relationship("FormboardLayout", back_populates="segments")
+
+
 class CustomConnector(Base):
     __tablename__ = "custom_connectors"
     id          = Column(Integer, primary_key=True, index=True)