Phase 2: Gmail IMAP fetch (IPv4), FR-2 source address, real mail in dashboard (AUD-67)

- internal/mailfetch: stdlib-only read-only IMAP client (LOGIN, SELECT,
  UID SEARCH, UID FETCH) that always dials tcp4; IPv6 to Gmail is broken
  from .13 and caused a socket EOF.
- MIME parsing to text, RFC2047 header decoding, FR-2 source address:
  X-Pm-Original-To -> To -> Received 'for <addr>' -> Return-Path, never
  Delivered-To. The matched header is recorded for audit.
- store: Message upsert/list/count + LogAction; schema migration v2 adds
  imap_uid and imap_uidvalidity.
- server: dashboard and /partials/inbox render real mail grouped by
  category with a recommended action; POST /actions/fetch runs a scan
  (CSRF-checked); nav counts; 'Check mail' button.
- config: GMAIL_USER, GMAIL_APP_PASSWORD, IMAP host/port/lookback/max.
- cmd: -fetch runs one scan and exits (n8n/CLI entry point, FR-1).
- compose/.env.example expose the Gmail + IMAP settings.
- tests: FR-2 precedence, MIME bodies, IMAP literal/parser, store
  upsert/migration, inbox rendering.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/config/config_test.go

@@ -7,6 +7,8 @@ func TestLoadDefaults(t *testing.T) {
 	for _, k := range []string{
 		"EMAIL_AGENT_ENV", "EMAIL_AGENT_ADDR", "EMAIL_AGENT_PORT",
 		"EMAIL_AGENT_DB_PATH", "EMAIL_AGENT_LOG_LEVEL", "EMAIL_AGENT_PUBLIC_BASE_URL",
+		"GMAIL_USER", "GMAIL_APP_PASSWORD", "EMAIL_AGENT_IMAP_HOST", "EMAIL_AGENT_IMAP_PORT",
+		"EMAIL_AGENT_IMAP_LOOKBACK_DAYS", "EMAIL_AGENT_IMAP_MAX_MESSAGES",
 	} {
 		t.Setenv(k, "")
 	}
@@ -27,6 +29,43 @@ func TestLoadDefaults(t *testing.T) {
 	if cfg.DBPath != DefaultDB {
 		t.Errorf("DBPath = %q, want %q", cfg.DBPath, DefaultDB)
 	}
+	if cfg.IMAPHost != DefaultIMAPHost {
+		t.Errorf("IMAPHost = %q, want %q", cfg.IMAPHost, DefaultIMAPHost)
+	}
+	if cfg.IMAPPort != DefaultIMAPPort {
+		t.Errorf("IMAPPort = %d, want %d", cfg.IMAPPort, DefaultIMAPPort)
+	}
+	if cfg.IMAPLookbackDays != DefaultIMAPLookbackDays {
+		t.Errorf("IMAPLookbackDays = %d, want %d", cfg.IMAPLookbackDays, DefaultIMAPLookbackDays)
+	}
+	if cfg.IMAPMaxMessages != DefaultIMAPMaxMessages {
+		t.Errorf("IMAPMaxMessages = %d, want %d", cfg.IMAPMaxMessages, DefaultIMAPMaxMessages)
+	}
+	if cfg.GmailConfigured() {
+		t.Error("GmailConfigured() = true with no credentials")
+	}
+}
+
+func TestGmailConfigured(t *testing.T) {
+	t.Setenv("GMAIL_USER", "samuelrolfe@gmail.com")
+	t.Setenv("GMAIL_APP_PASSWORD", "app-password")
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if !cfg.GmailConfigured() {
+		t.Error("GmailConfigured() = false with credentials set")
+	}
+
+	t.Setenv("GMAIL_APP_PASSWORD", "")
+	cfg, err = Load()
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+	if cfg.GmailConfigured() {
+		t.Error("GmailConfigured() = true with no app password")
+	}
 }
 
 func TestLoadOverrides(t *testing.T) {