Fonts: a new asset type, picked from the server or dropped in, worn by text objects (#74)

A font asset holds a file and nothing else, the twin of a texture: the server keeps it
content-addressed under data/fonts/{sha256}.{ext}, with the format read from the file's own
four-byte signature (finfo reports fonts inconsistently across libmagic versions). A text
wears one through its ordinary Font property, so overrides, reset, undo and the Properties
node come for free; no font means the editor's own typeface.

The picker lists everything the server holds and renders each row in the face it offers.
The family name is gm-font-<hash16>, never the name inside the file, so two "Regular" cannot
collide. WorldViewport.syncText is the single place that draws it, which covers scene, game
preview and play at once.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/debugHook.ts

@@ -6,6 +6,7 @@ import { activeDrag, Button, ui, Widget } from '../ui';
 import { shaderLibrary } from '../viewport/ShaderLibrary';
 import { textureLibrary } from '../viewport/TextureLibrary';
 import type { CentreTab, Editor } from './Editor';
+import { currentFontPicker } from './font/FontPicker';
 import { currentImagePicker } from './texture/ImagePicker';
 import type { EditorState } from './state';
 
@@ -303,6 +304,12 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
     /** The open image picker: what it offers, what is picked, and where a tile sits. */
     imagePicker: () => currentImagePicker()?.debugInfo() ?? null,
     imagePickerTile: (file: string) => currentImagePicker()?.tileGlobal(file) ?? null,
+    /** The same for the font picker, whose rows are the preview. */
+    fontPicker: () => currentFontPicker()?.debugInfo() ?? null,
+    fontPickerRow: (file: string) => currentFontPicker()?.rowGlobal(file) ?? null,
+    /** Which typeface a text ended up drawn in, and how wide it made it. */
+    textInfo: (id: string) => viewport.textInfo(id),
+    gameTextInfo: (id: string) => gameView.textInfo(id),
     texture: {
       current: () => textureEditor.currentAssetId,
       pickerWidth: () => textureEditor.picker.w,