feat: adapt to DSH 0.1.2-alpha.2 (npm-published) and bump to v0.17.2

DSH 0.1.2-alpha.2 is on npm under the `alpha` dist-tag, so the CI mount
pin and the @deepseek-ai/* devDependencies baseline move up from
0.1.1-rc.1/rc.2 (the dead dsh-client-runtime devDep goes away with
them). Verified end-to-end against a real 0.1.2-alpha.2 host: full
vitest suite (1106), typecheck, build/pack, consumer type surface, and
the headless mount smoke 14/14 — the token URL, slash RPC and
MarkdownText labels contracts are unchanged from alpha.1.

- dsh-settings dropped the runtime `settingsNamespace` export:
  namespaces are validated at compile time (SettingsNamespaceInput), so
  the host passes the 'dsh-better-sidebar' constant directly and the
  fake settings service in smoke.spec casts to the branded type.
- dsh-subagent bumped SUBAGENT_DESCRIPTOR_VERSION 2 -> 3: the version is
  stamped by the host package; the sidechat seed assertion now follows
  the constant instead of pinning a literal.
- Restored SessionEvent.ignorable and the RemoteError wrapping were
  verified to have no impact on this plugin.
- e2e scratch profiles (e2e-mount.sh / e2e-aggregate-mount.sh) add
  '@deepseek-ai/*' to minimumReleaseAgeExclude (mirroring the repo
  root): alpha releases are often <24h old when the lane runs, which
  pnpm 11's default minimumReleaseAge would refuse to install.
- vitest excludes .worktrees/** — local task worktrees carried stale
  code against the shared node_modules and broke on the devDeps bump.
- Version lockstep 0.17.2 (package.json, dsh.plugin.json,
  SIDEBAR_SERVICE_VERSION, README/AGENTS/guide docs).

.github/workflows/ci.yml

@@ -81,12 +81,11 @@ 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.
-      # NOTE: DSH 0.1.2-alpha.1 (Remote gateway slash endpoints + one-time-
-      # token browser auth) is NOT on npm yet — the lanes speak BOTH dialects
-      # (tests/e2e/host-protocol.ts, dot-first with slash fallback), so bump
-      # this pin once @deepseek-ai/dsh@0.1.2-alpha.1 publishes.
+      # DSH 0.1.2-alpha.x is published under the `alpha` dist-tag; the lanes
+      # speak BOTH RPC dialects (tests/e2e/host-protocol.ts, dot-first with
+      # slash fallback), so pre-alpha npm releases keep working too.
       - name: Install dsh CLI (pinned)
-        run: npm install -g @deepseek-ai/dsh@0.1.1-rc.2
+        run: npm install -g @deepseek-ai/dsh@0.1.2-alpha.2
 
       # lib/ is gitignored; the tarball is produced from this build.
       - name: Build and pack the npm tarball