feat: add is_bot_message column and support dedicated phone numbers (#235)

* feat: add is_bot_message column and support dedicated phone numbers

Replace fragile content-prefix bot detection with an explicit
is_bot_message database column. The old prefix check (content NOT LIKE
'Andy:%') is kept as a backstop for pre-migration messages.

- Add is_bot_message column with automatic backfill migration
- Add ASSISTANT_HAS_OWN_NUMBER env var to skip name prefix when the
  assistant has its own WhatsApp number
- Move prefix logic into WhatsApp channel (no longer a router concern)
- Remove prefixAssistantName from Channel interface
- Load .env via dotenv so launchd-managed processes pick up config
- WhatsApp bot detection: fromMe for own number, prefix match for shared

Based on #160 and #173.

Co-Authored-By: Stefan Gasser <stefan@stefangasser.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: extract shared .env parser and remove dotenv dependency

Extract .env parsing into src/env.ts, used by both config.ts and
container-runner.ts. Reads only requested keys without loading secrets
into process.env, avoiding leaking API keys to child processes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Stefan Gasser <stefan@stefangasser.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/ipc.ts

@@ -4,7 +4,6 @@ import path from 'path';
 import { CronExpressionParser } from 'cron-parser';
 
 import {
-  ASSISTANT_NAME,
   DATA_DIR,
   IPC_POLL_INTERVAL,
   MAIN_GROUP_FOLDER,
@@ -79,10 +78,7 @@ export function startIpcWatcher(deps: IpcDeps): void {
                   isMain ||
                   (targetGroup && targetGroup.folder === sourceGroup)
                 ) {
-                  await deps.sendMessage(
-                    data.chatJid,
-                    `${ASSISTANT_NAME}: ${data.text}`,
-                  );
+                  await deps.sendMessage(data.chatJid, data.text);
                   logger.info(
                     { chatJid: data.chatJid, sourceGroup },
                     'IPC message sent',