Gmail folder auto-advance + /forward command

- Reply-cycle auto-advance: staff reply files the thread to "Awaiting Reply",
  a customer response files it to "Needs Response" (new GMAIL_LABEL_AWAITING_REPLY
  / GMAIL_LABEL_NEEDS_RESPONSE labels + autoAdvanceFolder, which only moves
  threads still in the auto-cycle and leaves hand-filed folders alone)
- /forward: forward a ticket's email to another address (handlers/commands/forward.js
  + forward composition in services/gmail.js)
- Tests for the auto-advance cycle; label fixtures updated for the new labels

handlers/commands/forward.js

@@ -0,0 +1,59 @@
+/**
+ * /forward — forward this ticket's email thread to a third-party address.
+ *
+ * Builds a fresh outbound email to the target only; the original customer is
+ * never looped in (see services/gmail.js forwardThread).
+ */
+const { MessageFlags } = require('discord.js');
+const { findTicketForChannel } = require('../sharedHelpers');
+const { forwardThread } = require('../../services/gmail');
+const { logError, logTicketEvent } = require('../../services/debugLog');
+
+const plural = (n, word) => `${n} ${word}${n === 1 ? '' : 's'}`;
+
+async function handleForward(interaction) {
+  const ticket = await findTicketForChannel(interaction);
+  if (!ticket) return;
+
+  // Discord-origin tickets have no Gmail thread to forward.
+  if (ticket.gmailThreadId.startsWith('discord-')) {
+    return interaction.reply({
+      content: "This ticket has no email thread, so there's nothing to forward.",
+      flags: MessageFlags.Ephemeral
+    });
+  }
+
+  const target = interaction.options.getString('email');
+  const note = interaction.options.getString('note') || '';
+
+  // Defer: fetching the thread + downloading attachments can exceed the 3s window.
+  await interaction.deferReply({ flags: MessageFlags.Ephemeral });
+
+  try {
+    const { messageCount, attachmentCount, skipped } = await forwardThread(
+      ticket.gmailThreadId, target, note
+    );
+
+    logTicketEvent('Email thread forwarded', [
+      { name: 'To', value: target },
+      { name: 'Messages', value: String(messageCount) },
+      { name: 'Forwarded by', value: interaction.user.tag }
+    ], interaction).catch(() => {});
+
+    const skippedNote = skipped ? ` (${plural(skipped, 'attachment')} skipped — over the size limit)` : '';
+    return interaction.editReply({
+      content: `Forwarded ${plural(messageCount, 'message')} (${plural(attachmentCount, 'attachment')}) to **${target}**.${skippedNote}`
+    });
+  } catch (err) {
+    if (err.code === 'EBADRECIPIENT') {
+      return interaction.editReply({ content: "That doesn't look like a valid email address." });
+    }
+    if (err.code === 'EEMPTY') {
+      return interaction.editReply({ content: 'This thread has no messages to forward.' });
+    }
+    logError('handleForward', err, interaction).catch(() => {});
+    return interaction.editReply({ content: `Failed to forward: ${err.message}` });
+  }
+}
+
+module.exports = { handleForward };