fix(types): resolve all TypeScript compilation errors from non-null assertion removal

Fixes:
- chats.ts: revert encodeResult/initial to ! (guaranteed by callback assignment)
- groups.ts: fix operator precedence with ?? (wrap +attrs in parens), fix groupId type
- messages-recv.ts: extract messageKey.id to local const with fallback
- socket.ts: revert onClose! (guaranteed by synchronous callback assignment)
- event-buffer.ts: add 'notify' fallback for MessageUpsertType
- messages.ts: add filePath const after null guard, fix contextInfo type assertion
- noise-handler.ts: restore array index ! (guaranteed by length check)

Build now compiles with zero new errors.

https://claude.ai/code/session_01E2cfX1N3sJgCJBTvzGazSG

src/Utils/event-buffer.ts

@@ -1265,7 +1265,7 @@ function consolidateEvents(data: BufferedEventData) {
 
 	const messageUpsertList = Object.values(data.messageUpserts)
 	if (messageUpsertList.length) {
-		const type = messageUpsertList[0]?.type
+		const type = messageUpsertList[0]?.type ?? 'notify'
 		map['messages.upsert'] = {
 			messages: messageUpsertList.map(m => m.message),
 			type