feat(installer): add --locale flag for translated docs installation

Adds `--locale <code>` support to the ECC installer so users can install
localized reference docs (agents, commands, skills, rules) into
`~/.claude/docs/<locale>/` alongside the existing English installation.

Changes:
- manifests/install-modules.json: add 8 locale doc modules (docs-ja-JP,
  docs-zh-CN, docs-ko-KR, docs-pt-BR, docs-ru, docs-tr, docs-vi-VN,
  docs-zh-TW), each with kind="docs" and defaultInstall=false
- manifests/install-components.json: add 8 locale: components mapping to
  the new modules
- scripts/lib/install-manifests.js: add locale: family prefix,
  SUPPORTED_LOCALES, LOCALE_ALIAS_TO_COMPONENT_ID (with aliases like
  ja=ja-JP, zh=zh-CN, ko=ko-KR), and listSupportedLocales()
- scripts/lib/install/request.js: add --locale flag to parseInstallArgs(),
  resolve locale alias → component ID in normalizeInstallRequest(), throw
  on unsupported locale codes
- scripts/lib/install-targets/claude-home.js: map docs/<locale>/ source
  paths to ~/.claude/docs/<locale>/ destination (side-by-side, no overwrite
  of English files)
- scripts/install-apply.js: import listSupportedLocales, add --locale
  usage line and available locales list to --help output

Usage examples:
  ./install.sh --locale ja                    # Japanese docs only
  ./install.sh --profile core --locale zh-CN  # core profile + zh-CN docs
  ./install.sh typescript --locale ja         # legacy + locale (errors)

manifests/install-components.json

@@ -525,6 +525,70 @@
       "modules": [
         "machine-learning"
       ]
+    },
+    {
+      "id": "locale:ja",
+      "family": "locale",
+      "description": "Japanese (ja-JP) translated reference docs installed to ~/.claude/docs/ja-JP/.",
+      "modules": [
+        "docs-ja-JP"
+      ]
+    },
+    {
+      "id": "locale:zh-CN",
+      "family": "locale",
+      "description": "Simplified Chinese (zh-CN) translated reference docs installed to ~/.claude/docs/zh-CN/.",
+      "modules": [
+        "docs-zh-CN"
+      ]
+    },
+    {
+      "id": "locale:ko-KR",
+      "family": "locale",
+      "description": "Korean (ko-KR) translated reference docs installed to ~/.claude/docs/ko-KR/.",
+      "modules": [
+        "docs-ko-KR"
+      ]
+    },
+    {
+      "id": "locale:pt-BR",
+      "family": "locale",
+      "description": "Brazilian Portuguese (pt-BR) translated reference docs installed to ~/.claude/docs/pt-BR/.",
+      "modules": [
+        "docs-pt-BR"
+      ]
+    },
+    {
+      "id": "locale:ru",
+      "family": "locale",
+      "description": "Russian (ru) translated reference docs installed to ~/.claude/docs/ru/.",
+      "modules": [
+        "docs-ru"
+      ]
+    },
+    {
+      "id": "locale:tr",
+      "family": "locale",
+      "description": "Turkish (tr) translated reference docs installed to ~/.claude/docs/tr/.",
+      "modules": [
+        "docs-tr"
+      ]
+    },
+    {
+      "id": "locale:vi-VN",
+      "family": "locale",
+      "description": "Vietnamese (vi-VN) translated reference docs installed to ~/.claude/docs/vi-VN/.",
+      "modules": [
+        "docs-vi-VN"
+      ]
+    },
+    {
+      "id": "locale:zh-TW",
+      "family": "locale",
+      "description": "Traditional Chinese (zh-TW) translated reference docs installed to ~/.claude/docs/zh-TW/.",
+      "modules": [
+        "docs-zh-TW"
+      ]
     }
   ]
 }