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.

scripts/gen-cordis-catalog.ts

@@ -252,6 +252,7 @@ export const TYPE_LINK_EXEMPTIONS: Readonly<Record<string, string>> = {
   InsertTextRequest: 'event-local request contract is owned by packages/client/ui-slash/src/types.ts',
   AgentHandle: 'agent ownership handle is owned by packages/core/agent/README.md',
   AgentPreset: 'discovered preset record is owned by packages/preset/agent-presets/README.md',
+  PresetMetadata: 'preset display text is owned by packages/preset/agent-presets/README.md',
   BashEnvContributor: 'service-local extension type is owned by packages/bash/tool-bash/src/index.ts',
   BashEnvVariableInfo: 'service-local metadata type is owned by packages/bash/tool-bash/src/index.ts',
   CompactAgentContext: 'compaction service input is owned by packages/compact/compact/src/index.ts',