Rename Project to Diagram throughout the app

Per organized-ideas.md §8: the storage layer (DiagramRepository etc.) was
already renamed in an earlier phase; this finishes it everywhere else.

- domain/types.ts: Project -> Diagram. domain/project.ts -> domain/diagram.ts
  (createEmptyProject -> createEmptyDiagram, default name "Untitled Diagram").
- domain/compatibility.ts, domain/bom.ts: Project param/type -> Diagram.
- data/exportImport.ts: ProjectImportError -> DiagramImportError,
  projectToJson/downloadProjectFile/readProjectFile/normalizeProject -> their
  Diagram equivalents.
- state/projectStore.ts -> state/diagramStore.ts: useProjectStore ->
  useDiagramStore, the `project` field -> `diagram`, newProject/renameProject/
  importProject/applyRestoredProject -> *Diagram, restoredProjectUpdatedAt ->
  restoredDiagramUpdatedAt.
- Every component updated to match, compiler-guided (tsc -b enumerated each
  remaining call site after the core rename, the same approach used for the
  earlier catalog-parameter refactor).
- README updated for the terminology, and to match the repository class
  names (which had already been renamed but the README hadn't caught up).

No backend/schema changes: the JSON shape stored in diagrams.data never
changed, only TypeScript-side identifiers, so existing diagrams are
unaffected. One SQL comment fixed for accuracy (no migration needed).

Verified: tsc -b and oxlint clean; grepped src/ for any remaining
Project/project reference (none) after the sweep.

src/components/palette/DevicePalette.tsx

@@ -1,11 +1,11 @@
 import { useMemo, useState } from 'react'
 import { deviceTemplateToRow } from '../../data/catalogRowMapping'
-import { allDeviceCategories, allDeviceTemplates, hiddenDeviceTemplates } from '../../domain/project'
+import { allDeviceCategories, allDeviceTemplates, hiddenDeviceTemplates } from '../../domain/diagram'
 import type { DeviceTemplate } from '../../domain/types'
 import { useAdminReviewStore } from '../../state/adminReviewStore'
 import { useAuthStore } from '../../state/authStore'
 import { useCatalogStore } from '../../state/catalogStore'
-import { useProjectStore } from '../../state/projectStore'
+import { useDiagramStore } from '../../state/diagramStore'
 import { useSubmissionStore } from '../../state/submissionStore'
 import { TEMPLATE_DRAG_MIME } from '../canvas/FlowCanvas'
 import Chevron from '../common/Chevron'
@@ -19,10 +19,10 @@ type EditorTarget =
   | { mode: 'adminEdit'; template: DeviceTemplate }
 
 export default function DevicePalette() {
-  const project = useProjectStore((s) => s.project)
-  const access = useProjectStore((s) => s.access)
+  const diagram = useDiagramStore((s) => s.diagram)
+  const access = useDiagramStore((s) => s.access)
   const canEdit = access?.myPermission !== 'view'
-  const addDeviceFromTemplate = useProjectStore((s) => s.addDeviceFromTemplate)
+  const addDeviceFromTemplate = useDiagramStore((s) => s.addDeviceFromTemplate)
   const catalog = useCatalogStore((s) => s.catalog)
   const hiddenPublicIds = useCatalogStore((s) => s.hiddenPublicDeviceTemplateIds)
   const removeCustomDeviceTemplate = useCatalogStore((s) => s.removeCustomDeviceTemplate)
@@ -81,7 +81,7 @@ export default function DevicePalette() {
   const handleQuickAdd = (template: DeviceTemplate) => {
     if (!canEdit) return
     // Cascade placement so repeated quick-adds don't stack exactly on top of each other.
-    const offset = (project.devices.length % 8) * 24
+    const offset = (diagram.devices.length % 8) * 24
     addDeviceFromTemplate(catalog, template.id, { x: 80 + offset, y: 80 + offset })
   }