Give desktop users a real terminal for command-based setup

Some setup flows end in a shell command instead of a natural-language install path, so Settings now exposes a host PTY terminal backed by portable-pty and xterm. The terminal inherits the user's login-shell environment, forces a UTF-8 locale when needed, and preserves split UTF-8 output so Chinese paths render correctly.

Constraint: Desktop GUI apps do not inherit the user's interactive shell PATH on macOS.
Constraint: Command output may split UTF-8 characters across PTY reads.
Rejected: Use Tauri shell commands only | users need an interactive PTY for copy-pasted install flows.
Rejected: Ask users to edit shell profiles | terminal setup should work out of the box.
Confidence: high
Scope-risk: moderate
Directive: Keep terminal startup tied to host environment checks; do not bundle runtimes to solve PATH issues.
Tested: cargo fmt --check; cargo test --lib; cargo check; cd desktop && bun run lint; cd desktop && bun run test src/pages/TerminalSettings.test.tsx; cd desktop && bun run build; cd desktop && bun run build:macos-arm64
Tested: Computer Use verified npm is available in the built macOS app terminal and Chinese output renders after UTF-8 decoding fix.
Not-tested: Native Windows/Linux package runtime validation.

desktop/bun.lock

@@ -7,6 +7,8 @@
       "dependencies": {
         "@tailwindcss/typography": "^0.5.19",
         "@types/dompurify": "^3.2.0",
+        "@xterm/addon-fit": "^0.11.0",
+        "@xterm/xterm": "^6.0.0",
         "dompurify": "^3.3.3",
         "lucide-react": "^0.469.0",
         "marked": "^15.0.7",
@@ -470,6 +472,10 @@
 
     "@vitest/utils": ["@vitest/utils@3.2.4", "https://registry.npmmirror.com/@vitest/utils/-/utils-3.2.4.tgz", { "dependencies": { "@vitest/pretty-format": "3.2.4", "loupe": "^3.1.4", "tinyrainbow": "^2.0.0" } }, "sha512-fB2V0JFrQSMsCo9HiSq3Ezpdv4iYaXRG1Sx8edX3MwxfyNn83mKiGzOcH+Fkxt4MHxr3y42fQi1oeAInqgX2QA=="],
 
+    "@xterm/addon-fit": ["@xterm/addon-fit@0.11.0", "https://registry.npmmirror.com/@xterm/addon-fit/-/addon-fit-0.11.0.tgz", {}, "sha512-jYcgT6xtVYhnhgxh3QgYDnnNMYTcf8ElbxxFzX0IZo+vabQqSPAjC3c1wJrKB5E19VwQei89QCiZZP86DCPF7g=="],
+
+    "@xterm/xterm": ["@xterm/xterm@6.0.0", "https://registry.npmmirror.com/@xterm/xterm/-/xterm-6.0.0.tgz", {}, "sha512-TQwDdQGtwwDt+2cgKDLn0IRaSxYu1tSUjgKarSDkUM0ZNiSRXFpjxEsvc/Zgc5kq5omJ+V0a8/kIM2WD3sMOYg=="],
+
     "acorn": ["acorn@8.16.0", "https://registry.npmmirror.com/acorn/-/acorn-8.16.0.tgz", { "bin": { "acorn": "bin/acorn" } }, "sha512-UVJyE9MttOsBQIDKw1skb9nAwQuR5wuGD3+82K6JgJlm/Y+KI92oNsMNGZCYdDsVtRHSak0pcV5Dno5+4jh9sw=="],
 
     "agent-base": ["agent-base@7.1.4", "https://registry.npmmirror.com/agent-base/-/agent-base-7.1.4.tgz", {}, "sha512-MnA+YT8fwfJPgBx3m60MNqakm30XOkyIoH1y6huTQvC0PwZG7ki8NacLBcrPbNoo8vEZy7Jpuk7+jMO+CUovTQ=="],