feat: e opens a repo's SOPS or .env file, in nvim, sops edit or your editor (#1)

`e` on a file in a repo opens it; on a secret, it opens the file at that key's line.

- **SOPS files**: `sops edit` in the terminal, then back to lazysecrets with the keys reloaded. Exit 200 (nothing changed) shows "unchanged".
- **Other files inside nvim** (`$NVIM` set): lazysecrets asks that nvim, over `--remote-expr`, to open the file once lazysecrets' terminal closes, then quits. The file lands in the window you came from, not the closing float. Started from a shell in a terminal, it opens in the previous window straight away. No change to the nvim plugin is needed.
- **Otherwise**: `$VISUAL`/`$EDITOR` in the terminal (with `+N`, `file:N` or `-g file:N` for editors that take a line), else the system default app.

The repo provider now records each key's line (YAML node lines, env/ini line numbers) behind a new optional `provider.Files` interface. Other providers show "only SOPS and .env files in repos can be opened".

The nvim handoff was tested against a headless nvim 0.12: a floating terminal closed on exit the way snacks does, and a shell in a split. A file name with a space and a quote opened at the right line in both. Unit tests cover lines per format, the nvim, sops and default-app paths, and the editor line arguments.

Note: `e` is a new default key, so a config that already binds `e` to something else now gets the "bound to both" error, until one of them is rebound.

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #1

internal/ui/keys/keys.go

@@ -40,7 +40,7 @@ type Map struct {
 	Pane1, Pane2, Pane3, Pane4        key.Binding
 	NextTab, PrevTab                  key.Binding
 	Enter, Back, Filter               key.Binding
-	Reveal, Copy, CopyRef, Open       key.Binding
+	Reveal, Copy, CopyRef, Open, Edit key.Binding
 	Versions, Favourite, Favourites   key.Binding
 	Recent                            key.Binding
 	Note, Share, ShareMenu, OpenRef   key.Binding
@@ -111,6 +111,7 @@ func (m *Map) Actions() []Action {
 		a(Lists, "copyReference", &m.CopyRef, "copy reference", "secrets", "Copy the reference to use in config, e.g. @Microsoft.KeyVault(SecretUri=…) or {{secrets/scope/key}}."),
 		a(Lists, "versions", &m.Versions, "versions", "secrets", "List the versions of the selected item (Azure). Reveal, copy and share then act on the selected version."),
 		a(Lists, "openInBrowser", &m.Open, "open in browser", "secrets", "Open the selected subscription, vault or item in the browser (Azure portal or Databricks workspace)."),
+		a(Lists, "edit", &m.Edit, "open file", "secrets", "Open the selected SOPS or .env file, or the file of the selected secret at its line. SOPS files open with sops edit. Others open in the nvim lazysecrets runs in (quitting lazysecrets), else in $VISUAL or $EDITOR, else in the system's default app."),
 
 		a(Lists, "share", &m.Share, "copy link", "share", "Copy a lazysecrets:// link to the selected subscription, workspace, vault, scope or secret, for sharing. From the versions view the link is pinned to that version."),
 		a(Lists, "shareMenu", &m.ShareMenu, "share…", "share", "Choose what to share: the lazysecrets link, the plain Key Vault URL, the config reference, or the web page."),
@@ -183,7 +184,7 @@ var defaults = map[string][]string{
 	"lists.star": {"f"}, "lists.favourites": {"F"}, "lists.recent": {"R"}, "lists.search": {"ctrl+s"}, "lists.note": {"n"},
 	"lists.commands": {"x"},
 	"lists.reveal":   {"space"}, "lists.copyValue": {"y"}, "lists.copyReference": {"Y"},
-	"lists.versions": {"v"}, "lists.openInBrowser": {"o"},
+	"lists.versions": {"v"}, "lists.openInBrowser": {"o"}, "lists.edit": {"e"},
 	"lists.share": {"s"}, "lists.shareMenu": {"S"}, "lists.openLink": {"ctrl+o"},
 	"lists.dividerLeft": {"ctrl+left", "<"}, "lists.dividerRight": {"ctrl+right", ">"},
 	"lists.taller": {"ctrl+down", "}"}, "lists.shorter": {"ctrl+up", "{"},