feat: share env files as encrypted links

S → f on a repo, an env file or a key in one copies a
lazysecrets://share link holding the env files, encrypted (age) with
a secret's value: whoever can read that secret can open it. The key is
share.key in the repo's .lazysecrets.yaml, else in the config, else
picked when sharing; on Azure the link pins its version. Opening one
says what it holds, decrypts when asked, and saves the files in the
clone of the repo (or a folder chosen), replacing existing ones only
when asked. lazysecrets share prints a link from the command line.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/provider/provider.go

@@ -167,6 +167,13 @@ type Current interface {
 	Current(ctx context.Context) (Source, bool)
 }
 
+// Versioned is implemented by providers whose secrets have versions: it
+// is Value, also returning the version read (the current one when
+// o.Version is empty), so a link can pin it.
+type Versioned interface {
+	VersionedValue(ctx context.Context, o Object) (SecretValue, string, error)
+}
+
 // Locator is implemented by providers that can find where a container lives,
 // to open links. address is a vault host (kv.vault.azure.net) or a
 // workspace host. It returns the ID of the source holding it.
@@ -220,6 +227,10 @@ func (d *Denied) Error() string {
 
 func (d *Denied) Unwrap() error { return d.Err }
 
+// DetailPlainEnv is the Detail of a container that is a plain (not
+// encrypted) env file in a repo.
+const DetailPlainEnv = "env · plain text"
+
 // ContainerDetails is implemented by providers that can say more about a
 // container than its listing does: how a file is encrypted and what git
 // knows of it. ErrUnsupported means there's nothing more for c.