feat(i18n): add @fusion/i18n package, catalogs, and i18next-cli tooling (U2)

Create the @fusion/i18n package as the authored source-of-truth: shared
i18next config (namespace split, script-aware zh-CN/zh-TW fallback, plural
setup), en base catalogs, and a generated CLI static-import map so the
terminal surface is drop-in for new locales. Add the i18next-cli workflow
(extract/sync/types/status/lint) wired as root i18n:* scripts, install the
i18next stack into dashboard + CLI, strip @fusion/i18n from the published CLI
manifest, gitignore the generated dashboard catalog tree, and add a changeset.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -46,6 +46,12 @@
     "test:coverage:dashboard": "pnpm --filter @fusion/dashboard exec vitest run --silent=passed-only --reporter=dot --coverage",
     "test:slow-cli": "pnpm --filter @runfusion/fusion test:slow-cli",
     "typecheck": "pnpm -r --filter=!@fusion/desktop --filter=!@fusion/mobile typecheck",
+    "i18n:extract": "i18next-cli extract",
+    "i18n:sync": "i18next-cli sync",
+    "i18n:types": "i18next-cli types",
+    "i18n:status": "i18next-cli status",
+    "i18n:lint": "i18next-cli lint",
+    "i18n:gen-cli": "pnpm --filter @fusion/i18n gen:cli-catalogs",
     "changeset": "changeset",
     "version": "changeset version",
     "release": "node scripts/release.mjs",
@@ -76,6 +82,7 @@
     "@eslint/js": "^9.0.0",
     "eslint": "^9.0.0",
     "fast-glob": "^3.3.3",
+    "i18next-cli": "^1.59.1",
     "react-devtools-core": "^7.0.1",
     "tsx": "^4.19.0",
     "typescript": "^5.7.0",