feat: add profiles edit command

[TickTockBent]

Summary

Adds greywall profiles edit <name> so users can tweak saved profiles without hunting for the file path and hand-validating JSON.

• Opens the profile in $EDITOR (falls back to $VISUAL, then vi)
• Validates the edited JSON on close via config.Load
• On validation failure, prompts to re-edit or discard (restores original on discard)
• Handles editors with flags (code --wait, emacs -nw)
• Detects no-change exits early
• Catches empty profiles (config.Load returns nil for those)
• Updates profiles list output and parent help text to mention the new command

Closes #5

Test plan

• greywall profiles edit <saved-profile> opens editor, validates on close
• Invalid JSON after edit shows error and prompts re-edit/discard
• Discarding restores the original file content
• No-change edit prints "No changes made." and exits
• Empty file after edit is caught as validation error
• EDITOR="code --wait" works (split on whitespace)
• Profile not found gives clear error pointing to profiles list
• greywall profiles list footer now shows the edit hint

// squashing bugs, one cherry-pick at a time

[tito]

@TickTockBent thank you! Can you fix the lint that i can merge ?