feat(dsh): adapt to DSH 0.1.5-alpha.2

Baseline moves to DSH 0.1.5-alpha.2 only (peer floor ^0.1.5-alpha.2,
CI pin, manifest engines); alpha.1 users stay on v0.19.0-alpha.0.

Host-contract changes handled:
- the native guide entry lost its `description` field (entries are
  icon+title capsules now): `TabDescriptor.description` and the six
  `guideDesc*` keys plus the `nativeGuideDesc` fallback are removed.
- the file address grammar changed: `fileAddressFor` always returns a
  session-scoped address (absolute paths keep their leading `/`),
  `parseFileAddress` is prefix-based and strips `?`/`#`. The plugin's
  purity-gated mirror follows.
- global main panels replaced the `conversation` root slot with the
  keyed `main` slot (`main.conversation`): the bottom workbench's
  center-column locator now accepts both keys and skips
  `display: contents` slot hosts.

Fixes a pre-existing fill bug the alpha.2 probe made obvious: the native
tab body host is a block scroller with a definite height, so tab roots
that only declared `flex: 1` collapsed to content height and the side
chat composer drifted off the pane bottom. The native adapter now wraps
every tab body in a `height: 100%` column flex host.

Also promotes the dependencies `dsh-client-ui-primitives@0.1.5-alpha.2`
dropped from its manifest (anser / shiki / mdast-util-* / micromark-* /
katex / @shikijs/langs) and the newly unmet `dsh-session-persistence`
peer into devDependencies.

src/client/native/index.ts

@@ -43,7 +43,7 @@ interface NativeTabRegistry {
     priority?: 'extension' | 'builtin' | 'fallback'
     canOpen?: (address: string) => boolean
     title: (address: string) => string
-    guide?: readonly { order: number; title: () => string; description: () => string; icon?: unknown }[]
+    guide?: readonly { order: number; title: () => string; icon?: unknown }[]
   }): () => void
 }
 
@@ -63,17 +63,6 @@ function titleOf(descriptor: TabDescriptor): string {
   return typeof descriptor.title === 'function' ? descriptor.title() : descriptor.title
 }
 
-/**
- * The descriptor's guide line, evaluated fresh for the current locale. The
- * host's new-tab list renders one line per entry; without a declared
- * description every plugin page would read the same generic sentence.
- */
-function descriptionOf(descriptor: TabDescriptor | undefined): string {
-  const description = descriptor?.description
-  if (description === undefined) return t('nativeGuideDesc')
-  return typeof description === 'function' ? description() : description
-}
-
 /**
  * The guide row's glyph for a descriptor icon (nothing when it has none).
  * The native guide renders `entry.icon`, so a takeover registered without one
@@ -192,7 +181,6 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
             guide: [{
               order: descriptor.order ?? 100,
               title: () => titleOf(descriptor),
-              description: () => descriptionOf(descriptor),
               ...guideIconOf(icon),
             }],
           }),
@@ -219,7 +207,6 @@ export function registerNativeSurface(deps: NativeSurfaceDeps): () => void {
         guide: [{
           order: 10,
           title: () => t('files'),
-          description: () => descriptionOf(editor),
           // The takeover IS the editor descriptor's page, so it carries the
           // editor's glyph: without it the "Files" row is the only guide
           // entry with an empty icon slot.