fix: resolve Discord usernames to user IDs for outbound messages

When sending Discord messages via cron jobs or the message tool,
usernames like "john.doe" were incorrectly treated as channel names,
causing silent delivery failures.

This fix adds a resolveDiscordTarget() function that:
- Queries Discord directory to resolve usernames to user IDs
- Falls back to standard parsing for known formats
- Enables sending DMs by username without requiring explicit user:ID format

Changes:
- Added resolveDiscordTarget() in targets.ts with directory lookup
- Added parseAndResolveRecipient() in send.shared.ts
- Updated all outbound send functions to use username resolution

Fixes #2627

src/discord/send.outbound.ts

@@ -13,7 +13,7 @@ import {
   createDiscordClient,
   normalizeDiscordPollInput,
   normalizeStickerIds,
-  parseRecipient,
+  parseAndResolveRecipient,
   resolveChannelId,
   sendDiscordMedia,
   sendDiscordText,
@@ -49,7 +49,7 @@ export async function sendMessageDiscord(
   const chunkMode = resolveChunkMode(cfg, "discord", accountInfo.accountId);
   const textWithTables = convertMarkdownTables(text ?? "", tableMode);
   const { token, rest, request } = createDiscordClient(opts, cfg);
-  const recipient = parseRecipient(to);
+  const recipient = await parseAndResolveRecipient(to, opts.accountId);
   const { channelId } = await resolveChannelId(rest, recipient, request);
   let result: { id: string; channel_id: string } | { id: string | null; channel_id: string };
   try {
@@ -104,7 +104,7 @@ export async function sendStickerDiscord(
 ): Promise<DiscordSendResult> {
   const cfg = loadConfig();
   const { rest, request } = createDiscordClient(opts, cfg);
-  const recipient = parseRecipient(to);
+  const recipient = await parseAndResolveRecipient(to, opts.accountId);
   const { channelId } = await resolveChannelId(rest, recipient, request);
   const content = opts.content?.trim();
   const stickers = normalizeStickerIds(stickerIds);
@@ -131,7 +131,7 @@ export async function sendPollDiscord(
 ): Promise<DiscordSendResult> {
   const cfg = loadConfig();
   const { rest, request } = createDiscordClient(opts, cfg);
-  const recipient = parseRecipient(to);
+  const recipient = await parseAndResolveRecipient(to, opts.accountId);
   const { channelId } = await resolveChannelId(rest, recipient, request);
   const content = opts.content?.trim();
   const payload = normalizeDiscordPollInput(poll);