feat(vault-tui): implement KV client and service for managing secrets

- Added internal/vault/client.go for creating a Vault client with configuration settings.
- Introduced internal/vault/errors.go to classify Vault API errors for better UI handling.
- Created internal/vault/kv.go to manage KV secrets, including listing, reading, writing, and deleting operations.
- Implemented internal/vault/mounts.go to list and describe secret engine mounts.
- Developed internal/vault/service.go to provide a unified entry point for Vault operations.
- Added internal/vault/kv_test.go for comprehensive testing of KV operations.
- Introduced internal/ui/toast.go for transient notifications in the UI.
- Added renovate.json for dependency management and updates.

internal/ui/keys/help.go

@@ -0,0 +1,74 @@
+package keys
+
+import "charm.land/bubbles/v2/key"
+
+// screenHelp implements bubbles/help's Model.KeyMap with a fixed
+// short/full binding set — one instance per screen, built fresh from the
+// live *KeyMap so a `keys:` rebind or DisableWrites (read-only mode) is
+// reflected without the screen needing to know about it.
+type screenHelp struct {
+	short []key.Binding
+	full  [][]key.Binding
+}
+
+func (h screenHelp) ShortHelp() []key.Binding  { return h.short }
+func (h screenHelp) FullHelp() [][]key.Binding { return h.full }
+
+// BrowserHelp is the footer for the mounts/listing screens.
+func (k *KeyMap) BrowserHelp() screenHelp {
+	return screenHelp{
+		short: []key.Binding{k.Up, k.Down, k.Enter, k.Back, k.Filter, k.New, k.Help, k.Quit},
+		full: [][]key.Binding{
+			{k.Up, k.Down, k.Top, k.Bottom, k.Enter, k.Back},
+			{k.Filter, k.Refresh, k.New, k.Profiles, k.Logout},
+			{k.Help, k.Quit, k.ForceQuit},
+		},
+	}
+}
+
+// SecretHelp is the footer for the secret detail screen.
+func (k *KeyMap) SecretHelp() screenHelp {
+	return screenHelp{
+		short: []key.Binding{k.Up, k.Down, k.ToggleMask, k.CopyValue, k.Edit, k.Back, k.Help},
+		full: [][]key.Binding{
+			{k.Up, k.Down, k.Back, k.Versions},
+			{k.ToggleMask, k.ToggleMaskAll, k.CopyValue},
+			{k.Edit, k.Delete, k.Destroy},
+			{k.Help, k.Quit, k.ForceQuit},
+		},
+	}
+}
+
+// EditorHelp is the footer for the create/edit-secret screen.
+func (k *KeyMap) EditorHelp() screenHelp {
+	return screenHelp{
+		short: []key.Binding{k.Save, k.AddField, k.DeleteField, k.Cancel},
+		full: [][]key.Binding{
+			{k.Save, k.AddField, k.DeleteField, k.Cancel},
+		},
+	}
+}
+
+// VersionsHelp is the footer for the KV v2 version-history screen.
+func (k *KeyMap) VersionsHelp() screenHelp {
+	return screenHelp{
+		short: []key.Binding{k.Up, k.Down, k.Enter, k.Rollback, k.Undelete, k.Back},
+		full: [][]key.Binding{
+			{k.Up, k.Down, k.Enter, k.Back},
+			{k.Rollback, k.Undelete},
+			{k.Help, k.Quit, k.ForceQuit},
+		},
+	}
+}
+
+// AuthHelp is the footer for the auth-method picker phase (the form and
+// waiting phases use their own fixed, non-rebindable hints since tab/
+// enter/esc there are text-navigation, not KeyMap actions).
+func (k *KeyMap) AuthHelp() screenHelp {
+	return screenHelp{
+		short: []key.Binding{k.Up, k.Down, k.Enter, k.Quit},
+		full: [][]key.Binding{
+			{k.Up, k.Down, k.Enter, k.Quit, k.ForceQuit},
+		},
+	}
+}