Arcade/kiosk name flow, free cursor in menu and portable Linux export

Every game over unlocks the profile and frees the name, so the menu always asks
for a new player name: the field is empty at every boot, restart or game over and
the game does not start without a name (no anonymous scores). The player identity
is derived from the entered name (deterministic FNV-1a, 16 hex chars valid for the
public API) and the profile keeps the best score per name. Backend untouched.

Mouse: player._ready() captured the pointer before the menu existed, so the start
screen was not clickable. The cursor now always starts visible; the capture happens
only in player.begin_play(), called by start_game(). New `playing` flag gates Esc
and the Web click capture to the actual match.

Linux export preset: single-file x86_64 binary with the PCK embedded, no
libstdc++ dependency, official 4.7.1 template (glibc >= 2.28). Notes and the
export_presets.cfg `#`-is-not-a-comment trap documented in docs/KIOSK-ARCADE.md.

Tests: profile 30/30, start screen 15/15 (cursor free at menu, captured only in
game), boss 50/50, rebalance 14/14, touch 14 PASS, API 42/42, all other suites pass.

export_presets.cfg

@@ -28,3 +28,29 @@ html/canvas_resize_policy=2
 html/focus_canvas_on_start=true
 html/experimental_virtual_keyboard=true
 progressive_web_app/enabled=false
+
+[preset.1]
+name="Linux"
+platform="Linux"
+runnable=true
+advanced_options=false
+dedicated_server=false
+custom_features=""
+export_filter="all_resources"
+include_filter=""
+exclude_filter="addons/*,tools/*,docs/*,build/*,assets/**/*.mdl,assets/half_life_manifest.json"
+export_path="build/linux/work_death_balance.x86_64"
+patches=PackedStringArray()
+encrypt_pck=false
+encrypt_directory=false
+script_export_mode=2
+
+[preset.1.options]
+custom_template/release=""
+custom_template/debug=""
+debug/export_console_wrapper=1
+binary_format/embed_pck=true
+binary_format/architecture="x86_64"
+texture_format/s3tc_bptc=true
+texture_format/etc2_astc=false
+ssh_remote_deploy/enabled=false