fix: disable gruvbox in VMs, fix starship warnings, auto-detect browser

[maxrantil]

Summary

Fixes VM usability issues: gruvbox errors, starship warnings, and missing browser for gh CLI.

Problems Fixed

1. Gruvbox Colorscheme Error

Issue: init.vim tries to load gruvbox but it's not installed in minimal VM setups
Error: Vim shows colorscheme error on every startup
Fix: Disabled gruvbox plugin for VM setups (uses vim's default colorscheme)

2. Starship Git Status Warnings

Issue: Starship shows format string errors in git repos:
```
[WARN] - (starship::modules::git_status): Error parsing format string `git_status.stashed`
[WARN] - (starship::modules::git_status): Error parsing format string `git_status.untracked`
[WARN] - (starship::modules::git_status): Error parsing format string `git_status.modified`
```
Fix: Added `${count}` placeholder consistently to all git_status format strings

3. Browser Not Found (gh CLI)

Issue: gh CLI fails with:
```
! Failed opening a web browser at https://github.com/login/device
exec: "firefox": executable file not found in $PATH
```
Root Cause: BROWSER was hardcoded to `firefox` but VMs don't have it installed
Fix: Auto-detect available browser with priority:

1. chromium-browser (lightweight, good for VMs)
2. firefox
3. chromium
4. xdg-open (fallback)

Changes

• init.vim: Commented out gruvbox plugin and settings for minimal VM setup
• starship.toml: Fixed git_status format strings to use `${count}` consistently
• .zshenv: Changed BROWSER from hardcoded to auto-detected

Testing

✅ init.vim: No errors on vim startup
✅ starship: No warnings in git repositories
✅ BROWSER: Auto-detects available browser

VM Setup Notes

For gh CLI to work with browser in VMs:

1. Install chromium-browser:
   ```bash
   sudo apt install chromium-browser
   ```

2. Use X11 forwarding when SSH'ing:
   ```bash
   ssh -X -i ~/.ssh/vm_key user@vm-ip
   ```

3. Browser will open on host display:

   • gh CLI will launch chromium in VM
   • X11 forwards it to your host display
   • Authenticate in browser on your host

Impact

• Cleaner VM experience without plugin errors
• No more starship warnings
• gh CLI works out of the box with any installed browser
• Uses chromium instead of firefox in VMs (as preferred)