feat(pwsh): add the pwsh-local executor and the pwsh tool

Windows-native execution foundation: PwshLocalExecutor implements the bash
executor seam over ctx.subprocess (pwsh -NoLogo -NoProfile -NonInteractive
-Command, one argv element, no quoting layer; resolvePwshPath probes
PowerShell 7 / PATH / Windows PowerShell 5.1 as a pure function), and
tool-pwsh is the minimal PowerShell-dialect model-facing tool over ctx.bash
(foreground only, managed DSH_* env, timeout/signal/exit markers, terminal
and generic presenters). Both packages carry full suites (real pwsh,
self-skipping without it) at per-file 100% coverage; vitest's Windows
exclusion narrows from packages/bash/* to the bash-requiring packages so the
pwsh suites run natively on Windows too. The CLI gains the workspace deps
and tsconfig projects without mounting either plugin; the Windows-default
roadmap is recorded as a proposed Agent Note.

tsconfig.base.json

@@ -52,6 +52,8 @@
       "@deepseek-ai/dsh-session-title/client": ["./packages/session-title/session-title/src/client.ts"],
       "@deepseek-ai/dsh-plan-mode/types": ["./packages/plan/plan-mode/src/types.ts"],
       "@deepseek-ai/dsh-plan-mode/client": ["./packages/plan/plan-mode/src/client.ts"],
+      "@deepseek-ai/dsh-pwsh-local": ["./packages/bash/pwsh-local/src/index.ts"],
+      "@deepseek-ai/dsh-tool-pwsh": ["./packages/bash/tool-pwsh/src/index.ts"],
       "@deepseek-ai/dsh-goal/types": ["./packages/goal/goal/src/types.ts"],
       "@deepseek-ai/dsh-goal/client": ["./packages/goal/goal/src/client.ts"],
       "@deepseek-ai/dsh-llm/types": ["./packages/llm/llm/src/types.ts"],