feat: add wallet-scoped activity tag reads

[jvsena42]

Found while wiring hardware-wallet tag backup on Android (synonymdev/bitkit-android#1163, follow-up to #113). Verified against v0.5.5.

Problem

get_all_activities_tags() takes no wallet id, and the only scoped getter is get_tags(wallet_id, activity_id) for a single activity. There is no way to ask for "tags for wallet X", so apps fetch everything and filter in app code:

coreService.activity.getAllActivitiesTags()
    .filter { it.walletId == WalletScope.default }

That single line is the app's entire backup-scoping policy. It has already been added and removed once in Android, each time silently changing which wallet scopes leave the device — which matters, because these records go to a remote backup server.

Requested change

Expose get_activities_tags(wallet_id: Option<String>), where None returns every scope, so scoping becomes an explicit argument visible in review rather than an app-side filter. The same argument applies to get_all_pre_activity_metadata().

Acceptance criteria

• Tags can be read for a single wallet scope and for all scopes, without app-side filtering.
• The existing unscoped behaviour remains available.
• Tests cover scoped and unscoped reads, including a hardware trezor:{hash} scope.