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/types.ts

@@ -49,6 +49,7 @@ export interface NewMessage {
   content: string;
   timestamp: string;
   is_from_me?: boolean;
+  is_bot_message?: boolean;
 }
 
 export interface ScheduledTask {
@@ -86,10 +87,6 @@ export interface Channel {
   disconnect(): Promise<void>;
   // Optional: typing indicator. Channels that support it implement it.
   setTyping?(jid: string, isTyping: boolean): Promise<void>;
-  // Whether to prefix outbound messages with the assistant name.
-  // Telegram bots already display their name, so they return false.
-  // WhatsApp returns true. Default true if not implemented.
-  prefixAssistantName?: boolean;
 }
 
 // Callback type that channels use to deliver inbound messages