feat: snipemgr edit <integration> — open config in $EDITOR

[jackvaughanjr]

Summary

Add snipemgr edit <integration> to open the installed integration's settings.yaml (or Secret Manager secret) in $EDITOR. A shortcut for users who prefer direct config editing over the interactive wizard.

Motivation

The install wizard is good for first-time setup but cumbersome for small config tweaks. Power users who already know the config structure want to open the file directly and edit it — same as kubectl edit or git config --global -e.

Usage

snipemgr edit github2snipe
# Opens the integration's config in $EDITOR
# On save + quit, updated values are written back to Secret Manager

Behavior

1. Fetch the current config for github2snipe from Secret Manager
2. Write it to a temporary file (e.g. /tmp/snipemgr-github2snipe-<pid>.yaml)
3. Open $EDITOR (fallback: $VISUAL, then vi) with the temp file
4. On editor exit: diff the temp file against the original
5. If changed: prompt for confirmation, then write updated values back to Secret Manager
6. If unchanged: print "no changes" and exit
7. Always delete the temp file on exit (including on error/interrupt)

Acceptance criteria

• snipemgr edit <integration> opens the config in $EDITOR / $VISUAL / vi
• On save + quit, changed values are written back to Secret Manager
• If the editor exits without changes, no update is made
• The temp file is always cleaned up, including on Ctrl-C
• If the updated config fails validation (missing required fields), print the errors and prompt to re-edit or abort
• If the integration is not installed, print a clear error

Security notes

• The temp file contains plaintext credentials — write it to a directory with 0700 permissions and use 0600 file mode
• Delete the temp file with os.Remove in a defer block — ensure cleanup even on panic
• Do not log the temp file path at INFO level

Implementation notes

• No external dependency needed — exec.Command($EDITOR, tmpfile) with Stdin/Stdout/Stderr wired to os.Stdin/Stdout/Stderr is sufficient
• The temp file format should be YAML, matching settings.example.yaml structure