Editor Polish & OAuth Improvements

Broad set of fixes and improvements across the editor, terminal, settings, and authentication.

Improvements

• Replaced tauri-pty JS bindings with direct IPC invoke calls for more reliable terminal communication
• Migrated animation classes to Tailwind v4 theme tokens
• Bundled Pierre themes, grammars, and icons statically for Tauri builds
• Added hero screenshot to README

Fixes

• Reworked window close behavior to bypass ACL permission issues
• Fixed fish shell PATH format handling in sidecar
• Wired up download and install action in the About settings update button
• Improved OAuth token caching reliability in credential chain
• Corrected TaskCreate references and removed stale git stash instructions