ci: add Gitea Actions workflow with gofmt and test jobs

Add CI workflow at .gitea/workflows/ci.yml triggered on pull_request
with two jobs: fmt (gofmt check) and test (go test ./...).

Fix gofmt issues (import ordering) in 7 files so CI passes from
the start.

Fixes #7

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/config/config.go

@@ -102,17 +102,17 @@ func defaultCallbackBaseURL(listenAddr string) string {
 // validate checks that all required configuration values are present.
 func (c *Config) validate() error {
 	required := map[string]string{
-		"IMAP_HOST":              c.IMAPHost,
-		"IMAP_PORT":              c.IMAPPort,
-		"IMAP_USER":              c.IMAPUser,
-		"IMAP_PASS":              c.IMAPPass,
-		"SMTP_HOST":              c.SMTPHost,
-		"SMTP_PORT":              c.SMTPPort,
-		"SMTP_USER":              c.SMTPUser,
-		"SMTP_PASS":              c.SMTPPass,
-		"OPENCLAW_URL":           c.OpenClawURL,
-		"BRIDGE_CALLBACK_TOKEN":  c.BridgeCallbackToken,
-		"SYSTEM_EMAIL":           c.SystemEmail,
+		"IMAP_HOST":             c.IMAPHost,
+		"IMAP_PORT":             c.IMAPPort,
+		"IMAP_USER":             c.IMAPUser,
+		"IMAP_PASS":             c.IMAPPass,
+		"SMTP_HOST":             c.SMTPHost,
+		"SMTP_PORT":             c.SMTPPort,
+		"SMTP_USER":             c.SMTPUser,
+		"SMTP_PASS":             c.SMTPPass,
+		"OPENCLAW_URL":          c.OpenClawURL,
+		"BRIDGE_CALLBACK_TOKEN": c.BridgeCallbackToken,
+		"SYSTEM_EMAIL":          c.SystemEmail,
 	}
 
 	var missing []string