feat(agent-presets): give a preset a name and a description

A picker showed directory names, so the settings page could only ever list
`standard` / `core-web` / `cordis` and hope the reader knew what they meant.
A preset may now publish display text in an optional `preset.yml` beside
its composition, and the section renders cards — name, description, and the
one in use — instead of rows.

The file carries display text ONLY. `id` is the directory name and `trust`
comes from the root a preset was discovered under, so neither is writable
there: otherwise a locally authored preset could name itself into the
shipped set. It is a separate file because a composition is a top-level list
of plugin rows — YAML cannot carry sibling keys beside it, and a fake
metadata row would hand the Loader something to load.

Every read failure degrades to no metadata; absent, malformed, wrongly
typed, and blank all mean the same thing and the picker falls back to the
id. Presentation is not capability: a preset whose name is broken still
mounts.

The editor gained name and description fields above the YAML, and clearing
both removes the file rather than storing a blank name.

packages/preset/agent-presets/src/index.ts

@@ -16,6 +16,7 @@ import z from 'schemastery'
 import { settingsNamespace, type SettingsScope } from '@deepseek-ai/dsh-settings'
 import { discoverPresets } from './discovery.ts'
 import { deleteComposition, readComposition, writeComposition } from './authoring.ts'
+import type { PresetMetadata } from './metadata.ts'
 import { mountPreset, serviceForAgent, unmountPresetFor } from './mount.ts'
 import { PresetNotWritableError } from './authoring.ts'
 import { UnknownPresetError, type AgentPreset, type Config } from './types.ts'
@@ -35,6 +36,9 @@ export const AgentPresetSettingsSchema: z<AgentPresetSettings> = z.object({
 })
 
 export { COMPOSITION_FILE, discoverPresets, scanRoot } from './discovery.ts'
+export {
+  METADATA_FILE, readPresetMetadata, renderPresetMetadata, type PresetMetadata,
+} from './metadata.ts'
 export {
   inactiveRows, leakedServices, livePresetMounts, mountPreset, serviceForAgent,
   unmountPresetFor, type PresetMount,
@@ -171,17 +175,18 @@ export class AgentPresets extends Service {
    * names a missing plugin still fails at the next session that selects it.
    * @param id - the preset id, which becomes its directory name.
    * @param content - the composition text.
+   * @param metadata - display name and description; clearing both removes the file.
    * @throws when the id is unusable, the text is not an entry list, or the
    * deployment configures no writable root.
    */
-  async write(id: string, content: string): Promise<void> {
+  async write(id: string, content: string, metadata: PresetMetadata = {}): Promise<void> {
     // A shipped preset belongs to the deployment: overwriting it would remove
     // the known-good composition a broken local one is compared against.
     const existing = (await this.list()).find(preset => preset.id === id)
     if (existing !== undefined && existing.trust !== 'user') {
       throw new PresetNotWritableError(id, 'it ships with the deployment')
     }
-    await writeComposition(this.config.roots, id, content)
+    await writeComposition(this.config.roots, id, content, metadata)
   }
 
   /**