feat: add delete message feature + comprehensive bug fixes

- Add WhatsApp-style delete modal with "Delete for everyone" / "Delete for me" / "Cancel"
- "Delete for everyone" disabled when any selected message is not fromMe
- "Delete for me" always removes locally regardless of API result
- Delete available from context menu (single msg) and select-mode toolbar (multi-select)
- Fix chatApiCall to send body on DELETE requests (was silently dropped)
- Fix chatState missing allFetchedMessages initialisation (crash before first convo)
- Fix modal not closing on conversation switch or close (wrong JID bug)
- Fix Escape key not dismissing delete modal
- Fix select toolbar delete button uses stable id instead of fragile attribute selector
- Fix RTL: add dir=auto to contact/poll/default/quoted message text elements
- Fix XSS: onerror avatar uses sibling-element pattern instead of innerHTML
- Fix XSS: quotedMsg.id sanitised before embedding in onclick
- Fix XSS: image lightbox uses data-src attribute instead of inline URL
- Fix crash: location case guards against null m.text + uses encodeURIComponent
- Fix: group name/subject/desc escaped with chatEsc() + dir=auto added
- Fix: FileReader base64 split guarded against missing comma
- Fix chatCopySelected / chatForwardSelected use Set.has() instead of Array.includes()
- Fix chatCloseConversation resets select mode state

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

Author: erancybersec