Add mobile view-only support

Below md width, the app now forces view-only (same canEdit mechanism as a
shared view-only diagram) rather than trying to support touch editing:
palette and inspector panels hide, editing controls disable, and the top
bar collapses to just Diagrams + Account. A bottom tab bar swaps between a
full-screen canvas and a full-screen Bill of Materials, since there's no
room for both side by side. Canvas gets a few mobile-specific trims too:
MiniMap and the interactivity lock button hide whenever canEdit is false
(the lock button doesn't actually grant editing either way — nodesDraggable/
nodesConnectable already override it — so leaving it visible would just be
misleading), and h-screen is replaced with h-dvh throughout so the layout
doesn't get clipped by a mobile browser's collapsing address bar.

Also fixes quick-add's anti-stack offset (24px — far smaller than a device
node) to actually tile devices apart instead of leaving them nearly
overlapping, and logs a deferred "Auto-arrange" layout feature in
organized-ideas.md, surfaced by mobile visitors having no way to fix an
overlapping diagram themselves.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017DUU6CnxECCDeqDNYJgr5x

src/components/inspector/ConnectionInspector.tsx

@@ -2,12 +2,12 @@ import { useMemo, useState } from 'react'
 import { allCableTypes, cableTypesForConnection, getPortType } from '../../domain/diagram'
 import { useCatalogStore } from '../../state/catalogStore'
 import { useDiagramStore } from '../../state/diagramStore'
+import { useCanEdit } from '../../hooks/useCanEdit'
 
 export default function ConnectionInspector({ connectionId }: { connectionId: string }) {
   const diagram = useDiagramStore((s) => s.diagram)
   const catalog = useCatalogStore((s) => s.catalog)
-  const access = useDiagramStore((s) => s.access)
-  const canEdit = access?.myPermission !== 'view'
+  const canEdit = useCanEdit()
   const updateConnection = useDiagramStore((s) => s.updateConnection)
   const removeConnection = useDiagramStore((s) => s.removeConnection)
   const startBundle = useDiagramStore((s) => s.startBundle)