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/router.ts

@@ -1,4 +1,3 @@
-import { ASSISTANT_NAME } from './config.js';
 import { Channel, NewMessage } from './types.js';
 
 export function escapeXml(s: string): string {
@@ -20,12 +19,10 @@ export function stripInternalTags(text: string): string {
   return text.replace(/<internal>[\s\S]*?<\/internal>/g, '').trim();
 }
 
-export function formatOutbound(channel: Channel, rawText: string): string {
+export function formatOutbound(rawText: string): string {
   const text = stripInternalTags(rawText);
   if (!text) return '';
-  const prefix =
-    channel.prefixAssistantName !== false ? `${ASSISTANT_NAME}: ` : '';
-  return `${prefix}${text}`;
+  return text;
 }
 
 export function routeOutbound(