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.shared.ts

@@ -13,7 +13,7 @@ import type { ChunkMode } from "../auto-reply/chunk.js";
 import { chunkDiscordTextWithMode } from "./chunk.js";
 import { fetchChannelPermissionsDiscord, isThreadChannelType } from "./send.permissions.js";
 import { DiscordSendError } from "./send.types.js";
-import { parseDiscordTarget } from "./targets.js";
+import { parseDiscordTarget, resolveDiscordTarget } from "./targets.js";
 import { normalizeDiscordToken } from "./token.js";
 
 const DISCORD_TEXT_LIMIT = 2000;
@@ -101,6 +101,44 @@ function parseRecipient(raw: string): DiscordRecipient {
   return { kind: target.kind, id: target.id };
 }
 
+/**
+ * Parse and resolve Discord recipient, including username lookup.
+ * This enables sending DMs by username (e.g., "john.doe") by querying
+ * the Discord directory to resolve usernames to user IDs.
+ *
+ * @param raw - The recipient string (username, ID, or known format)
+ * @param accountId - Discord account ID to use for directory lookup
+ * @returns Parsed DiscordRecipient with resolved user ID if applicable
+ */
+export async function parseAndResolveRecipient(
+  raw: string,
+  accountId?: string,
+): Promise<DiscordRecipient> {
+  const cfg = loadConfig();
+  const accountInfo = resolveDiscordAccount({ cfg, accountId });
+
+  // First try to resolve using directory lookup (handles usernames)
+  const resolved = await resolveDiscordTarget(raw, {
+    cfg,
+    accountId: accountInfo.accountId,
+  });
+
+  if (resolved) {
+    return { kind: resolved.kind, id: resolved.id };
+  }
+
+  // Fallback to standard parsing (for channels, etc.)
+  const parsed = parseDiscordTarget(raw, {
+    ambiguousMessage: `Ambiguous Discord recipient "${raw.trim()}". Use "user:${raw.trim()}" for DMs or "channel:${raw.trim()}" for channel messages.`,
+  });
+
+  if (!parsed) {
+    throw new Error("Recipient is required for Discord sends");
+  }
+
+  return { kind: parsed.kind, id: parsed.id };
+}
+
 function normalizeStickerIds(raw: string[]) {
   const ids = raw.map((entry) => entry.trim()).filter(Boolean);
   if (ids.length === 0) {