fix(zaps): collapse same-actor zap spam in notifications and post drawer

[dmnyc]

Summary

Android counterpart to iOS PR barrydeen/wisp-ios#161.

A sender spamming many small zaps against the same note used to push everything else off-screen — both in the Notifications tab (one row per zap receipt) and in the in-post engagement drawer (one row per individual zapper). This change folds same-actor + same-note zaps into a single row in both surfaces.

Notifications tab

• FlatNotificationItem gains mergedZaps: List<FlatNotificationItem> (defaulted empty so the ingest path is unchanged) and a totalZapSats computed property summing the primary + every merged duplicate.
• NotificationsViewModel.collapseSameActorZapSpam runs after the existing filter pass. Walks the newest-first list, dedupes NotificationType.ZAP entries by (actorPubkey, referencedEventId), and folds duplicates into the primary's mergedZaps. DM_ZAP / PROFILE_ZAP don't participate — they have no referencedEventId to dedupe against.
• NotificationTypeIcon bolt-icon label uses totalZapSats so the surfaced amount is the combined contribution from this actor on this note.
• ZenNotificationRow shows a +N more pill next to the actor name when duplicates were folded.
• New MergedZapsBreakdown composable renders below the embedded referenced note (matching the iOS NotificationRowView caption order): N zaps · total sats header, then one line per individual zap with amount + comment.

Post-engagement drawer

• ReactionDetailsSection now groups [ZapDetail] by pubkey before rendering. Each group renders one ZapRow with the combined sat total and a (×N) count suffix on the label when N > 1. The first non-empty zap message becomes the row label (falls back to display name / shortened npub same as the per-zap default).
• Distinct zappers still get their own rows; sort stays "highest combined sats first."
• Long-press inspect on a collapsed row routes to the first individual receipt in the group, preserving the existing single-receipt affordance.

Test plan

• On a note that's been zapped repeatedly by the same actor, the Notifications tab shows ONE row for that actor with the +N more pill; expanding the row shows the embedded note followed by the per-zap breakdown (N zaps · total sats + one line per zap with amount and comment).
• The notification's bolt-icon label shows the combined sat total, not just the first zap's amount.
• DM_ZAP and PROFILE_ZAP notifications (no referencedEventId) still render as individual rows.
• In the post-engagement drawer, the same actor's repeat zaps collapse into one row with (×N) after the label and the combined sat total on the right.
• Different zappers on the same note continue to render as separate rows, sorted by combined sats descending.
• Long-press on a collapsed row in the drawer opens the inspect modal for the first individual receipt (existing behavior preserved).