feat(dsh): adapt to DSH 0.1.5-rc.2 (baseline pin advance, v0.19.1)

The pinned baseline moves to DSH 0.1.5-rc.2 (npm `next`; `latest` is still
rc.1) while the plugin's peer floor stays ^0.1.5-rc.1, so rc.1 hosts need no
DSH upgrade to run this version. Nothing in the rc.1 -> rc.2 delta touches
this plugin: of 300 changed upstream files, the overwhelming majority are
single-line `version` bumps in per-package package.json files, and the only
real code edits are the message-feedback dialog, deliverables card CSS and
the CodeFileIcon SVG artwork split (`code-file-icon-artwork.ts`). There are
zero changes under packages/api|host|session|agent and zero type-surface
changes beyond one line in message-feedback/types.ts, so the adaptation is
the pin itself — devDependencies, the CI mount lane and
SIDEBAR_SERVICE_VERSION — with no plugin-side code change and no runtime
compatibility layer.

- package.json: devDependency pins 0.1.5-rc.1 -> 0.1.5-rc.2 (including
  dsh-client-locale, which is still published on the DSH tuple); peers keep
  the ^0.1.5-rc.1 floor; version -> 0.19.1
- dsh.plugin.json: version -> 0.19.1; engines.dsh keeps >=0.1.5-rc.1 (same
  supported range as the peer floor — the two must not fork)
- pnpm-lock.yaml: lockfile realigned to rc.2
- src/client/service.ts: SIDEBAR_SERVICE_VERSION -> 0.19.1 (tests/service.spec.ts
  asserts it equals package.json's version)

Verified locally on macOS arm64 against the rc.2 tree: pnpm install clean,
`pnpm peers check` reports no peer dependency issues, typecheck / lint /
check:consumer-types green, `pnpm test` 126 files / 1312 passed / 9 skipped.
The real-mount smoke (scripts/e2e-mount.sh with DSH_CMD pinned to rc.2) and
the aggregate double-mount lane both pass — evidence recorded in
docs/plans/2026-09-10-dsh-0.1.5-rc.2-adaptation.md.

src/client/service.ts

@@ -165,7 +165,7 @@ export interface TabDescriptor {
   /**
    * One-line description of what this tab shows, rendered under the title in
    * the host's new-tab list (DSH's native right Sidebar guide page). DSH
-   * 0.1.5-rc.1 renders descriptions only while the guide lists at most 4
+   * 0.1.5-rc.1+ renders descriptions only while the guide lists at most 4
    * entries — a longer list drops every description and shows titles alone —
    * and a descriptor that declares none renders the title by itself (the
    * host no longer substitutes a generic fallback, so declare the real
@@ -529,7 +529,7 @@ export function matchUrlTarget(tabs: readonly TabDescriptor[], url: URL): TabDes
  * The plugin version this service instance reports. Keep in lockstep with
  * `package.json`'s version — `tests/service.spec.ts` asserts the pair.
  */
-export const SIDEBAR_SERVICE_VERSION = '0.19.0'
+export const SIDEBAR_SERVICE_VERSION = '0.19.1'
 
 /**
  * Monotonic capability list consumers use to gate new API usage (features