feat: e on the status pane edits the config (#55)

`e` on the status pane (`0`) opens your config file, as in lazygit's status panel. The status footer shows it as `e edit config`. There's no global key. It opens the config the same way `e` opens a local file:
- inside nvim, in that nvim (lazysecrets quits);
- otherwise in `$VISUAL` or `$EDITOR`, coming back after;
- otherwise in the system's default app.

It opens the first config file: your own, also when `--config` layers several. A config that doesn't exist yet is created with a comment linking to its docs. Closing the editor says "restart lazysecrets to use it", since the config is read at startup.

Docs: keys.md (status pane) and config.md. Tested: the default app with a new config, nvim with an existing one left unchanged, the restart message, and the footer.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Reviewed-on: #55
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

docs/config.md

@@ -2,7 +2,9 @@
 
 Optional, at `~/.config/lazysecrets/config.yaml` (or
 `$XDG_CONFIG_HOME/lazysecrets/config.yaml`, or `--config`). Flags override
-it. Unknown keys are an error, so typos don't go unnoticed.
+it. Unknown keys are an error, so typos don't go unnoticed. `e` on the
+status pane (`0`) opens it in your editor, as in lazygit (making it if
+it isn't there yet); changes apply when lazysecrets starts again.
 
 ```yaml
 icons: true            # Nerd Font icons (v3+); also --icons=false or LAZYSECRETS_ICONS=0