chat: run the /email chat from the email account's storage dir

The email chat's working directory now resolves to
DATA_PATH/<owner>/email_accounts/<accountEmail> (created if missing), so the agent
operates in the selected account's dir (emails.db, attachment_cache, …).

- websocket.ts: new resolveChatCwd — context 'email' → the account dir (via a new
  resolveEmailCwd), 'chat' → the pwd/claude_sessions dir, else the given cwd. Both the
  Claude and OpenCode handlers use it. The account defaults to the owner's first enabled
  account for now; the account selector will pass it as contextId later.
- OpenCode honors the cwd again: send-opencode passes it as the session `directory`
  (client.createSession(directory?)) for context-scoped chats; the general /chat still
  omits it and uses the fixed server's default project. Verified against the live server
  that directory-bound sessions create + list.

No frontend change — the /email panel already sends context:'email'.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/channels/send-opencode.ts

@@ -45,7 +45,7 @@ export async function sendOpenCodeStreaming(params: OpenCodeStreamingParams): Pr
     (params.sessionKey.startsWith('ses_') ? params.sessionKey : undefined) ??
     params.resumeSessionId;
   if (!opencodeSessionId) {
-    opencodeSessionId = await conn.createSession();
+    opencodeSessionId = await conn.createSession(params.cwd);
   }
   setOpenCodeSession(params.sessionKey, opencodeSessionId);
   const sessionId = opencodeSessionId;