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/agent-presets.schema.ts

@@ -14,6 +14,8 @@ export const agentPresetEntrySchema = z.object({
   id: z.string().min(1),
   trust: z.union([z.literal('system'), z.literal('user')]),
   isDefault: z.boolean(),
+  name: z.string().optional(),
+  description: z.string().optional(),
 }) satisfies z.ZodType<Wire<AgentPresetEntry>>
 
 /** agentPreset.list request payload. */
@@ -48,12 +50,16 @@ export const agentPresetReadValueSchema = z.object({
   trust: z.union([z.literal('system'), z.literal('user')]),
   content: z.string(),
   writable: z.boolean(),
+  name: z.string().optional(),
+  description: z.string().optional(),
 }) satisfies z.ZodType<Wire<ResponseValue<'agentPreset.read'>>>
 
 /** agentPreset.write request payload. */
 export const agentPresetWriteRequestSchema = z.object({
   agentPreset: z.string().min(1),
   content: z.string(),
+  name: z.string().optional(),
+  description: z.string().optional(),
 }) satisfies z.ZodType<Wire<RequestPayload<'agentPreset.write'>>>
 
 /** agentPreset.write response value. */