Add vim support to agentos-shell

[NathanFlurry]

vim is not available in just shell today (the shell only loads the coreutils/git/curl/etc. software set; there is no editor).

Needed

• Package vim (or a vim-compatible editor) as a WASM registry-software package in secure-exec registry/software/.
• Add it to the agentos-shell software list (packages/shell/src/main.ts) so it's on PATH in just shell.

Notes

• vim is a large/complex C program; compiling it to wasm32-wasip1 (curses + termios over the guest PTY) is non-trivial. A lighter vim-like editor may be a pragmatic first step.
• Depends on the PTY work in the native shell (full-screen TUI apps need correct winsize/resize — see the crossterm size() follow-up).

Part of making just shell a complete interactive environment.