Re-mint watchpr's Gitea token when it expires

Vault-minted Gitea tokens last ~1h, far less than a watch, and every poll
past expiry 401'd into a warning while watchpr looked healthy.

- retry a rejected request once with a freshly minted token
- abort the watch when the fresh token is rejected too
- poll anonymously when no token can be minted, mint only on a real 401/403

internal/agent/token.go

@@ -86,17 +86,31 @@ func AuthentikURL() string {
 }
 
 var (
-	tokenOnce  sync.Once
-	tokenValue string
-	tokenErr   error
+	tokenMu     sync.Mutex
+	tokenMinted bool
+	tokenValue  string
+	tokenErr    error
 )
 
 // GiteaToken returns a Gitea token, minting it via Vault AppRole on first call
 // and caching it in-process for the lifetime of the command.
 func GiteaToken() (string, error) {
-	tokenOnce.Do(func() {
+	tokenMu.Lock()
+	defer tokenMu.Unlock()
+	if !tokenMinted {
 		tokenValue, tokenErr = fetchGiteaToken(VaultAddr(), RoleID(), GiteaCredsPath())
-	})
+		tokenMinted = true
+	}
+	return tokenValue, tokenErr
+}
+
+// RefreshGiteaToken mints a fresh Gitea token and replaces the cached one, for
+// callers that outlive the ~1h token TTL.
+func RefreshGiteaToken() (string, error) {
+	tokenMu.Lock()
+	defer tokenMu.Unlock()
+	tokenValue, tokenErr = fetchGiteaToken(VaultAddr(), RoleID(), GiteaCredsPath())
+	tokenMinted = true
 	return tokenValue, tokenErr
 }