Change the graphics protocol N key from a boolean into a usage-hints
bitmask. Define the first bit as a transient hint, allowing the terminal
to treat the image data as short-lived and apply optimizations such as
skipping disk cache writes.
Propagate the transient hint through frame coalescing and composition, so
a composed frame is transient if any contributing frame is transient.
Add a new graphics protocol key, N=1, to request that transmitted
image/frame data is kept only in memory and not written to the graphics
disk cache file.
This is useful for transient high-frequency updates such as video-like
streams, where the latest frame is the only useful data and persisting
each frame to the disk cache causes unnecessary write traffic.
The implementation keeps the existing graphics cache abstraction intact:
memory-only entries can still be read back by animation, composition, and
frame coalescing paths. Only persistence to the disk cache file is skipped.
The default behavior is unchanged when N is omitted or set to zero.
Always do a roundtrip at kitten exit, except for special purpose
kittens. This slows down exit by one round trip time (capped at 2
seconds), however it ensures that we never get terminal response leak.
Fixes#9839
Add --allow-fallback option to the map command that controls shifted
and ascii (alternate_key) fallback for individual key mappings.
For non-Latin keyboard layouts, when the current layout key is
non-ascii (codepoint > 127 and < 0xE000), the alternate_key from
the base layout is used for matching if the mapping opts in via
--allow-fallback=shifted,ascii.
Default kitty bindings use --allow-fallback=shifted,ascii so they
work out of the box with non-Latin layouts. User custom mappings
default to --allow-fallback=shifted (preserving existing shifted_key
behavior without ascii fallback).
--allow-fallback=none disables all fallback for a mapping.
Python side: parse_options_for_map() in options/utils.py handles flag
parsing, ShortcutMapping uses it in __init__. get_shortcut() filters
candidates by per-mapping allow_fallback.
Go side: ParseMap() handles --allow-fallback, KeyAction stores
AllowFallback, ShortcutTracker.Match passes it to matching.
MatchesParsedShortcut defaults to shifted,ascii for hardcoded shortcuts.
Migrated kittens (themes, command_palette, diff, choose_files) to
use ShortcutTracker with configurable map entries.
Tests added for Python (5 test methods) and Go (ParseMap + key matching).
