feat(app): hide the window with ⌘W

[liukun]

Closes #12

Summary

Bind ⌘W to hide the window.

• Escape walks the dismiss cascade and, in vim mode, deliberately stops short of hiding, so :q was the only way to put the note away from the keyboard.
• ⌘W is the macOS key for closing a window and already closes the Settings window, so it is the natural key here.
• The new HideWindow action runs the same Intent::Hide as :q and the Hide Window command, closing any open panel before hiding, so the three stay in step. The command is now labelled ⌘W under :.
• Escape's behaviour is unchanged. Settings still takes ⌘W first through its deeper key context.

Tests

• cmd_w_hides_the_window_in_every_mode_but_closes_settings_first in e2e/vim.rs: ⌘W resolves to HideWindow in vim normal, vim insert and non-vim mode, and to CloseSettings under the Settings context. It checks keymap resolution only, since the test platform cannot hide a window.
• the_table_gives_every_surface_the_same_labels now asserts Intent::Hide is labelled ⌘W and :wq (Then[Save, Hide]) has no label.
• cargo clippy --all-targets -- -D warnings is clean. The five e2e tests that fail on this branch also fail on master at 165bd2c, unrelated to this change.