feat: pick the share key in Go to, or by reference

Sharing without share.key opens Go to as a picker of secrets instead
of asking for a link: it lists only secrets, enter picks one, and a
pasted reference picks it too. The key, there and in share.key or
--key, can be a secret's lazysecrets:// link, Key Vault URL or
@Microsoft.KeyVault(...) reference.

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

docs/links.md

@@ -49,15 +49,20 @@ az keyvault secret set --vault-name kv-team --name env-share --value "$(openssl
 ```
 
 and name it in the repo's `.lazysecrets.yaml` (committed: the whole team
-uses it) or your config (for repos that don't name one), or pick one when
-sharing:
+uses it) or your config (for repos that don't name one), by its
+`lazysecrets://` link, Key Vault URL or `@Microsoft.KeyVault(...)`
+reference:
 
 ```yaml
 share:
-  key: lazysecrets://azure/kv-team.vault.azure.net/secrets/env-share
+  key: https://kv-team.vault.azure.net/secrets/env-share
 ```
 
-On the command line, `lazysecrets share [--key <link>] <env file>...`
+With neither, sharing asks which secret, in [Go to](keys.md#go-to): it
+lists only secrets, and `enter` picks one (pasting a reference picks it
+too).
+
+On the command line, `lazysecrets share [--key <secret>] <env file>...`
 prints the link.
 
 Opening a share link says which repo it's from, how many files and which