fix(tci): subscribe to the radio's meters; fix the new-spot count; explain an SMTP refusal

TCI meters: the S-meter came only from RX_SMETER and the transmit meters from
TX_POWER / TX_SWR — commands ExpertSDR3 does not send. The protocol's answer is
a subscription (RX_SENSORS_ENABLE / TX_SENSORS_ENABLE, §4.4 of the TCI PDF),
after which the radio pushes RX_CHANNEL_SENSORS and TX_SENSORS. Nobody had
asked, so the console's meters sat empty in RX and in TX while everything else
worked.

Cluster: the held-spot counter looked for the row it froze on. A station spotted
again REPLACES its row, so that row vanishes in the ordinary course of things
and the count fell through to 'everything is new' — 4, 5, then 500. Counted by
timestamp now, which survives both the replacement and the ring buffer.

SMTP: '535 5.7.139 basic authentication is disabled' is a policy, not a typo.
The message now says so, and says what actually helps, without claiming a policy
when the server simply rejected the password.

internal/email/email.go

@@ -5,6 +5,7 @@ package email
 import (
 	"fmt"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/wneessen/go-mail"
@@ -86,12 +87,42 @@ func SendFiles(cfg Config, to, subject, body string, attachPaths []string) error
 		return fmt.Errorf("smtp client: %w", err)
 	}
 	if err := client.DialAndSend(m); err != nil {
-		return fmt.Errorf("send via %s:%d (%s, %s): %w",
-			cfg.Host, cfg.Port, cfg.Encryption, describeSize(attachPaths), err)
+		return fmt.Errorf("send via %s:%d (%s, %s): %w%s",
+			cfg.Host, cfg.Port, cfg.Encryption, describeSize(attachPaths), err, explainSMTP(err))
 	}
 	return nil
 }
 
+// explainSMTP turns a server's refusal into the thing to go and do.
+//
+// A rejection is quoted verbatim above it — the server's own words are the
+// evidence — but several of them name a policy rather than a mistake, and no
+// amount of re-checking the password will fix those. Microsoft's is the one
+// operators keep hitting: basic authentication for SMTP is switched off across
+// Microsoft 365 and outlook.com, and an app password does not bring it back.
+func explainSMTP(err error) string {
+	msg := strings.ToLower(err.Error())
+	switch {
+	case strings.Contains(msg, "basic authentication is disabled"),
+		strings.Contains(msg, "5.7.139"):
+		return "\n\nMicrosoft has switched off password-based SMTP for this account. " +
+			"An app password does not restore it — the server refuses the password itself, not the one you typed. " +
+			"On a Microsoft 365 tenant an administrator can re-enable it for this mailbox " +
+			"(Set-CASMailbox -SmtpClientAuthenticationDisabled $false, plus the tenant-wide setting); " +
+			"otherwise use another provider for alerts (a Gmail account with an app password works, so does any ordinary IMAP/SMTP host)."
+	case strings.Contains(msg, "application-specific password"),
+		strings.Contains(msg, "5.7.9"):
+		return "\n\nThis account needs an APP PASSWORD rather than the one you sign in with " +
+			"(Google, Yahoo and others require it once two-factor authentication is on)."
+	case strings.Contains(msg, "5.7.8"), strings.Contains(msg, "authentication failed"),
+		strings.Contains(msg, "535"):
+		return "\n\nThe server rejected the username or the password."
+	case strings.Contains(msg, "must issue a starttls"):
+		return "\n\nThe server requires encryption: set STARTTLS (usually port 587) or SSL (465)."
+	}
+	return ""
+}
+
 // describeSize reports what was attached, in bytes.
 //
 // "An existing connection was forcibly closed" during DATA is the same message

internal/email/email_explain_test.go

@@ -0,0 +1,29 @@
+package email
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestExplainSMTP(t *testing.T) {
+	// The real refusal, from an operator's Outlook account.
+	outlook := errors.New("SMTP AUTH failed: 535 5.7.139 Authentication unsuccessful, basic authentication is disabled.")
+	if got := explainSMTP(outlook); !strings.Contains(got, "Microsoft has switched off") {
+		t.Errorf("the Microsoft policy refusal is not explained: %q", got)
+	}
+	// A plain wrong password must NOT claim a policy: the advice would send the
+	// operator to an administrator over a typo.
+	wrong := errors.New("535 5.7.8 authentication failed")
+	got := explainSMTP(wrong)
+	if strings.Contains(got, "Microsoft") {
+		t.Errorf("a wrong password was explained as a Microsoft policy: %q", got)
+	}
+	if !strings.Contains(got, "rejected the username") {
+		t.Errorf("a wrong password is not explained: %q", got)
+	}
+	// Anything else is left to speak for itself.
+	if got := explainSMTP(errors.New("dial tcp: i/o timeout")); got != "" {
+		t.Errorf("an unrelated error got an explanation: %q", got)
+	}
+}