feat: Nerd Font support, clipboard paste, and PTY environment fixes

- Add ttyd-nerd-font submodule with embedded JetBrains Mono Nerd Font
  for proper icon rendering in browser via ttyd
- Add Ctrl+Shift+V / Shift+Insert paste support in ttyd frontend
- Strip Zellij env vars from PTY child processes to prevent workspace
  terminal from inheriting Zellij session context
- Launch PTY commands through login shell for proper PATH resolution
- Use /etc/passwd shell lookup instead of $SHELL (Zellij overrides it)
- Soften ANSI 256-color palette to match modern dark themes
- Handle Nerd Font PUA glyphs as width 1 in pyte terminal emulator
- Fix brightmagenta typo in pyte graphics
- Update install script to build ttyd from submodule source
- Add web deployment TODO items for image paste and context menu

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "deploy/ttyd-nerd-font"]
+	path = deploy/ttyd-nerd-font
+	url = https://github.com/metorm/ttyd-nerd-font.git