fix: prevent context menu from dismissing on trackpad press release

[TigerInYourDream]

Summary

Fixes #57

On macOS trackpad, right-clicking via two-finger press caused the context menu to flash and immediately disappear. This affected both the room context menu and the message context menu.

Root Cause

macOS trackpad generates a FingerScroll(0, 0) event on two-finger press. Both menus had Hit::FingerScroll(_) => true which unconditionally closed on any scroll event, including zero-scroll.

Fix (two layers)

Layer 1 — FingerScroll zero-scroll filter (direct fix):

// Before: any scroll closes
Hit::FingerScroll(_) => true,

// After: only real scrolls close
Hit::FingerScroll(fse) => fse.scroll.x != 0.0 || fse.scroll.y != 0.0,

Layer 2 — ContextMenuOpenGesture (defense-in-depth):

Tracks the digit_id + capture_time of the gesture that opened the menu. If a FingerUp arrives matching this gesture, it's consumed instead of treated as "click outside". This protects against edge cases where:

• The menu position is adjusted for window bounds (the FingerUp lands outside main_content)
• The finger drifts slightly between press and release

The capture_time matching is verified correct via Makepad source: FingerDown.time is stored as capture.time during capture_digit(), then read back as FingerUp.capture_time.

Changes

• src/home/mod.rs — ContextMenuOpenGesture struct (digit_id + capture_time) and consume_context_menu_opening_finger_up() shared utility
• src/home/room_context_menu.rs — Track opening gesture, filter zero-scroll FingerScroll
• src/home/new_message_context_menu.rs — Same fix for message context menu
• src/home/rooms_list_entry.rs — Pass ContextMenuOpenGesture in SecondaryClicked action
• src/home/rooms_list.rs — Forward gesture through OpenRoomContextMenu action
• src/home/room_screen.rs — Pass gesture through OpenMessageContextMenu action
• src/app.rs — Forward gesture to show() calls

Test plan

• macOS trackpad: two-finger tap on room → context menu stays open
• macOS trackpad: two-finger press on room → context menu stays open (was broken)
• macOS trackpad: two-finger press on message → message context menu stays open
• Click outside menu → menu closes normally
• Press Escape → menu closes normally
• Scroll (real scroll with non-zero delta) → menu closes normally
• Long-press on room (mobile gesture) → context menu stays open after release