fix: use native clipboard manager for terminal paste on Linux

[Pandaboizu]

Title: fix(terminal): use native clipboard manager for terminal copy/paste on Linux

Summary

This fixes a Linux terminal clipboard issue where Ctrl+Shift+V only works if
the copied text originated inside Terax itself.

Problem

On Linux, the terminal paste path was using:

• navigator.clipboard.readText()

That appears to work for clipboard content Terax wrote itself, but not
reliably for clipboard content copied from external applications.

Repro

1. Copy text inside Terax
2. Paste with Ctrl+Shift+V
3. Works
4. Copy text from Firefox or another app
5. Paste with Ctrl+Shift+V
6. Fails

Fix

• Add @tauri-apps/plugin-clipboard-manager
• Use native clipboard read/write for the terminal copy/paste path
• Keep the web clipboard API as fallback
• Add focused regression tests for the fallback behavior

Files changed

• src/modules/terminal/lib/rendererPool.ts
• src/modules/terminal/lib/clipboard.ts
• src/modules/terminal/lib/clipboard.test.ts
• package.json
• pnpm-lock.yaml
• src-tauri/Cargo.toml
• src-tauri/Cargo.lock
• src-tauri/src/lib.rs
• src-tauri/capabilities/default.json

Validation

• pnpm test src/modules/terminal/lib/clipboard.test.ts
• pnpm check-types
• local production build completed successfully

Notes

This is a terminal clipboard boundary issue, not a PTY issue. Internal copy
working while external copy fails points at the webview clipboard layer rather
than shell or terminal transport.