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/fake/repos.go

@@ -35,7 +35,7 @@ func Repos() *Provider {
 	// commit are what git says of it: "tracked", "ignored" or "untracked".
 	file := func(src provider.Source, path, method, git, commit string, kv ...string) {
 		sops := method != ""
-		detail := "env · plain text"
+		detail := provider.DetailPlainEnv
 		if sops {
 			detail = "sops · " + method
 		}