[FEATURE] iOS share sheet: let me send a file to an existing chat or Code session

When I open a PDF in Mail on iPhone, tap Share and choose Claude, the app always starts a new conversation. There is no way to pick an existing chat or an active Claude Code session.

WhatsApp, Telegram, Slack and other chat apps all show a list of recent conversations in their share extension, so the file lands where the work already is.

Expected: the Claude share extension lists recent chats and active Code sessions (with a "New chat" option at the top), and sends the file into the one I pick.

Why it matters: I work with Claude Code sessions from my phone. Starting a new session loses all context, so today the only workaround is saving the file to Files first and then attaching it from inside the session. That extra save step is exactly what every other messaging app avoids.

Platform: iOS, Claude app