Move global item collected-state, deadzone, and story flags into save file

Adds three new pieces of save-file state, all following the same shape:
the save file is the single source of truth, not a separate live runtime
copy that gets synced in/out.

- globalitemstore.h/.c: per-global-entity-ID "collected" flags
  (savefile_t.globalItemCollected), so a global item entity's init
  callback can check whether it was already picked up in a prior session
  without needing to keep the entity itself alive to remember that.

- Gamepad deadzone: removed input_t.deadzone entirely. The setting UI and
  every platform's actual deadzone-applying code (inputGetDeadzoneDolphin/
  SDL2, previously hardcoded per-platform literals that the settings menu
  didn't actually affect) now read savefile_t.deadzone directly via
  saveGet(SAVE_ACTIVE_SLOT). Default lives in savefile.h
  (SAVE_DEADZONE_DEFAULT), stamped onto every slot in saveInit().

- Story flags: STORY_FLAG_VALUES (a live, codegen-initialized array) is
  replaced by savefile_t.storyFlags, read/written via the existing
  storyFlagGet()/storyFlagSet() call sites (now macros/functions over the
  active save file instead of a separate array). tools/story.py now
  generates STORY_FLAG_DEFAULTS (const) instead; storyFlagInitDefaults()
  stamps those onto a save the first time it's used (file->exists false),
  called from rpgInit().

Added SAVE_ACTIVE_SLOT (0) to savefile.h as the one shared "which slot is
actually being played" constant, replacing three different local/implicit
0s (uigamemenu.c, rpg.c, and now the settings/input call sites).

Verified round-trip on Linux (all three together in one save/load cycle);
both Linux and PSP build clean.

src/dusklinux/input/inputlinux.c

@@ -6,6 +6,7 @@
  */
 
 #include "input/input.h"
+#include "save/save.h"
 
 inputbuttondata_t INPUT_BUTTON_DATA[] = {
   #ifdef DUSK_INPUT_GAMEPAD
@@ -547,5 +548,5 @@ errorret_t inputInitLinux(void) {
 }
 
 float_t inputGetDeadzoneSDL2(const inputbutton_t button) {
-  return 0.17f;
+  return saveGet(SAVE_ACTIVE_SLOT)->deadzone;
 }