fix(agent-presets,web): broken presets are roster rows, not gaps

A hand-damaged preset was silent until the worst moment. An unparsable
composition listed as an ordinary selectable row and failed only at the
next session start — set as default, every new session failed. A
directory whose composition file was deleted vanished from the roster
while still occupying its id: copy answered "delete the existing preset
first" while remove answered "not found", a dead end.

Discovery now owns health: every id-shaped directory is a roster slot,
broken when its composition is missing or unloadable, checked with the
loader's own entryListSchema dialect (!!js included) so health never
rejects what the loader accepts. `broken` rides AgentPreset, the
agentPreset.list entry, and the UI row; mount/recompose/standingKeyFor
refuse broken up front with the discovery-reported reason, while
resolve/read/remove still answer. The section renders marked red cards —
unselectable, uncopyable, deletable, location kept on custom rows — and
both pickers drop broken rows entirely.

The cordis preset's persona now forbids editing the shipped install
(corrupting cordis would disable the mode itself) and points authoring
at $DSH_HOME/.agent-presets; its skill teaches preset.yml metadata, the
copy-first workflow, the one-escalation sandbox reality, and honest
verification. Exercised live: asked to edit the shipped composition the
composed agent refuses citing both rules; asked for real presets (simple
and complex) it lands them under the user root with one approved
escalation each and self-checks with the loader dialect.

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

@@ -17,16 +17,7 @@ import { dirname, isAbsolute, join, resolve } from 'node:path'
 import { writeFileAtomic } from '@deepseek-ai/dsh-atomic-write'
 import { expandHomePath } from '@deepseek-ai/dsh-paths'
 import { METADATA_FILE, renderPresetMetadata } from './metadata.ts'
-import type { AgentPreset, PresetRoot } from './types.ts'
-
-/**
- * Ids a preset directory may use.
- *
- * The id becomes a path segment, so this is a containment boundary rather than
- * a style rule: `..`, a separator, or an absolute-looking name would place the
- * composition outside the root the deployment authorised.
- */
-const PRESET_ID = /^[a-z0-9][a-z0-9-]*$/
+import { PRESET_ID, type AgentPreset, type PresetRoot } from './types.ts'
 
 /** A preset id that cannot be used as a directory name under a root. */
 export class InvalidPresetIdError extends Error {