feat: Station Control amp parity + all amps, Help→Send log to F4BPO, bulk-edit frequency, fix Cluster midnight sort

- Station Control: the amplifier panel is now the exact same card as the FlexRadio panel (extracted shared AmpCard: OPERATE/STANDBY, ON/OFF, power level, output-power bar, live FWD/ID/temp meters). Every configured amp gets its own card — no dropdown.
- Help → "Send log to F4BPO" (only when SMTP is configured): e-mails opslog.log + previous session + crash log to the developer. New email.SendFiles for multi-attachment.
- Bulk edit: new "Frequency (MHz)" field sets freq_hz AND recomputes band; out-of-band values rejected. Fixes a run logged on a stale/default freq after CAT dropped.
- Cluster: Time column sorted lexically on the HHMMZ string, so spots after 0000Z sorted below 2359Z and looked frozen at the UTC rollover. Now sorts by real arrival time.
- Also folds in the DVK auto-CQ/2-column layout and Station Control dashboard batch (changelog 0.20.10, EN+FR).

internal/email/email.go

@@ -41,6 +41,16 @@ func (c Config) opts() []mail.Option {
 
 // Send delivers a plain-text email to `to`, optionally attaching a file.
 func Send(cfg Config, to, subject, body, attachPath string) error {
+	var attach []string
+	if attachPath != "" {
+		attach = []string{attachPath}
+	}
+	return SendFiles(cfg, to, subject, body, attach)
+}
+
+// SendFiles is like Send but attaches any number of files (missing paths are
+// skipped by the mail library at send time).
+func SendFiles(cfg Config, to, subject, body string, attachPaths []string) error {
 	if cfg.Host == "" {
 		return fmt.Errorf("SMTP server not configured")
 	}
@@ -65,8 +75,10 @@ func Send(cfg Config, to, subject, body, attachPath string) error {
 	}
 	m.Subject(subject)
 	m.SetBodyString(mail.TypeTextPlain, body)
-	if attachPath != "" {
-		m.AttachFile(attachPath)
+	for _, p := range attachPaths {
+		if p != "" {
+			m.AttachFile(p)
+		}
 	}
 	client, err := mail.NewClient(cfg.Host, cfg.opts()...)
 	if err != nil {