fix: backend code review fixes for network diagrams

- Replace legacy Optional imports with modern str | None syntax
- Type JSONB columns as Mapped[list[dict[str, Any]]]
- Escape SQL LIKE wildcards (%, _) in diagram search
- Type DiagramNode.position as Position(x, y) Pydantic model
- Wrap AI response parsing in KeyError handler for clean 422 errors
- Remove unused Optional/TYPE_CHECKING imports from schemas/models
- Extract _get_available_slugs helper to DRY duplicate queries

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CURRENT-STATE.md

@@ -2,7 +2,7 @@
 
 > **Purpose:** Quick-reference file showing exactly where the project stands.
 > **For Claude Code:** Read this first to understand what's done and what's next.
-> **Last Updated:** April 4, 2026
+> **Last Updated:** April 4, 2026 (evening)
 
 ---
 
@@ -215,6 +215,22 @@
 - **ConcludeSessionModal copy refresh** — Forward-facing action verbs, "Close & Generate" CTA, consistent outcome labels
 - Deleted unused FlowPilotActionBar component (227 lines dead code)
 
+### Network Diagrams (In Progress)
+
+- Network diagram editor with React Flow (@xyflow/react v12) canvas
+- Device node system: 27 device types across 7 categories (network, compute, storage, cloud, endpoint, infrastructure, security)
+- Custom device type creation via DeviceToolbar
+- Connection edges with 6 types (ethernet, fiber, wifi, vpn, vlan, wan) — color-coded, dashed for wireless/VPN
+- Properties panel for editing device and connection details
+- AI-assisted diagram generation (describe network → auto-layout)
+- Auto-save every 30 seconds, manual save, JSON export
+- **React Flow UI Components** — Cherry-picked and Charcoal-restyled: BaseNode (structured header/content/footer slots), BaseHandle (styled connection handles), LabeledHandle (named port labels), NodeStatusIndicator (status border effect: emerald/red/yellow), NodeTooltip (hover details via NodeToolbar), LabeledGroupNode (subnet/VLAN/site/DMZ containers), AnimatedSvgEdge (traffic flow visualization)
+- Grouping category in toolbar: Subnet, VLAN, Site, DMZ drag-drop to canvas
+- Traffic flow toggle on edges (switches between static and animated)
+- Context menu with copy/paste/duplicate/select all shortcuts
+- Drop position uses `screenToFlowPosition()` for correct placement at any zoom/pan level
+- **Bug fix:** PropertiesPanel inputs now work — selection uses IDs instead of stale object snapshots
+
 ### Maintenance Flows (Hidden from UI)
 
 - Batch session launch, saved target lists