feat(dsh): adapt to DSH 0.1.5-rc.1 and restore the guide description

Baseline moves to DSH 0.1.5-rc.1 — the 0.1.5 line's first release
candidate, and the npm `latest` dist-tag now: peer floor ^0.1.5-rc.1,
devDependency pins, the CI mount-lane pin and dsh.plugin.json engines
all follow. 0.1.5-alpha.2 users stay on v0.19.0-alpha.1.

The upstream delta from alpha.2 is small: 373 changed files, mostly
version bumps, sidebar preview polish and test snapshots. Exactly two
changes touch this plugin, and only one needs work:

- `SidebarRightGuideEntry.description` is back (optional). The native
  guide renders it only while it lists at most 4 entries; a longer list
  drops every description. The plugin restores `TabDescriptor.description`
  and the six built-in `guideDesc*` lines (20 dictionaries) verbatim from
  0b6ac5d^, but deliberately does NOT restore the old generic
  `nativeGuideDesc` fallback: the host has no fallback of its own, so a
  descriptor that declares none now ships no `description` field at all
  and renders as a clean title-only capsule.

  Consequence worth knowing: the plugin contributes six guide entries, so
  the default composition is over the 4-entry limit and shows titles only.
  The mount lane proves the restored field end to end by shrinking the
  enabled set to three types through the plugin's own settings route
  (scratch profile only) and requiring the Files capsule to grow its line.

- The built-in `files` type declares a guide description again and uses a
  coloured folder glyph; the plugin owns that kind, so nothing to do.

Verified unchanged from alpha.2 (so nobody re-checks them): the global
main-panel model, the file address grammar (util/workspace-path changed
only its package.json), the native tab-body host contract (.paneBody is
still a block scroller with a definite height), the core/agent/session/
subagent host APIs and the ui-primitives export surface.

Restore caveat fixed in the lane: the settings route merges patches
key-wise, so undoing a temporary `tabsEnabled` change by posting the
original (empty) map leaves the disabled keys behind — the e2e restores
every key it touched explicitly.

.github/workflows/ci.yml

@@ -131,10 +131,11 @@ jobs:
       # Pin the DSH CLI the lane mounts into; the profile's bundle stack
       # (dsh-base / dsh-web-app) resolves from this installation. Keep in
       # step with the plugin's @deepseek-ai/* peer range when bumping.
-      # DSH 0.1.5-alpha.2 is published under the `alpha` dist-tag; the lanes
-      # speak the slash-only RPC dialect (tests/e2e/host-protocol.ts).
+      # DSH 0.1.5-rc.1 is the `latest` (and `next`) dist-tag on npm — the
+      # 0.1.5 line's first release candidate; the lanes speak the slash-only
+      # RPC dialect (tests/e2e/host-protocol.ts).
       - name: Install dsh CLI (pinned)
-        run: npm install -g @deepseek-ai/dsh@0.1.5-alpha.2
+        run: npm install -g @deepseek-ai/dsh@0.1.5-rc.1
 
       # lib/ is gitignored; the tarball is produced from this build.
       - name: Build and pack the npm tarball