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/host/apiproxy/src/api-proxy.ts

@@ -2544,6 +2544,8 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
             id: preset.id,
             trust: preset.trust,
             isDefault: preset.id === defaultId,
+            ...preset.name === undefined ? {} : { name: preset.name },
+            ...preset.description === undefined ? {} : { description: preset.description },
           })),
           authorable: presets.authorable,
         })
@@ -2615,6 +2617,8 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
             trust: preset.trust,
             content: await presets.read(preset.id),
             writable: preset.trust === 'user' && presets.authorable,
+            ...preset.name === undefined ? {} : { name: preset.name },
+            ...preset.description === undefined ? {} : { description: preset.description },
           })
         } catch (error: unknown) {
           return err(request, presetError(agentPreset, error))
@@ -2622,11 +2626,14 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
       },
 
       async write(request) {
-        const { agentPreset, content } = request.payload
+        const { agentPreset, content, name, description } = request.payload
         const presets = ctx.get('agentPresets')
         if (presets === undefined) return err(request, noRoster(agentPreset))
         try {
-          await presets.write(agentPreset, content)
+          await presets.write(agentPreset, content, {
+            ...name === undefined ? {} : { name },
+            ...description === undefined ? {} : { description },
+          })
           return ok(request, { agentPreset })
         } catch (error: unknown) {
           return err(request, presetError(agentPreset, error))