Add doctor diagnostic command for bootstrap failure investigation

[Copilot]

User asked whether we can locally verify that the $alias: syntax under $ErrorActionPreference="Stop" is the actual root cause of the wh not recognized bootstrap failure.

Changes

• bin/doctor.ps1 — diagnostic script that spawns isolated pwsh subprocesses to:
  • Test $alias:tp = 'Test-Path' under $ErrorActionPreference="Stop" (reproduces the failure condition)
  • Check for pre-existing read-only aliases conflicting with tp/sc
  • Dot-source aliases.ps1 under Stop mode and verify all helpers (wh, mkd, mkl, isadmin, tp, sc) are defined
  • Check bootstrap dependency commands (pwsh, git, scoop, cargo)
• cli/definitions.toml — register doctor as a [[script]] so dotcli generate exposes it as a shell function
• pwsh/aliases.ps1 — fix stray double-space on line 1

Example output

=== $alias: syntax under ErrorActionPreference=Stop ===
  [FAIL] $alias: 構文が Stop モードで失敗: ERR:...
  [INFO] → これが wh not recognized の原因です

=== aliases.ps1 dot-source テスト (Stop モード) ===
  [PASS] aliases.ps1 の全ヘルパーが定義済み: wh,mkd,mkl,isadmin,tp,sc

On environments where the issue doesn't reproduce, the first check passes with a note to check for alias conflicts manually.

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