feat: restore last game folder/rom position on reset-to-menu (#87)

[Xeroxxx]

May close: #87

Reset to menu got extended with two more options: Rom and Folder

• Rom drops back to last folder and the cursor is on the rom previously launched.
• Folder drops back to the folder where the last rom was launched from.
• On/Off unchanged
• Only on Warmboot/Reset
• Coldboot behavior stays unchanged.

https://www.youtube.com/watch?v=pQI8CDfdafI

[spend-cloud-tom]

Reset-to-menu in Folder/Rom mode lands one folder short for paths a few levels deep

Repro: put a ROM at /A/B/C/D/E/Game.smc, set Reset to menu = Folder, run it, short-reset. The menu opens in /A/B/C/D/ instead of /A/B/C/D/E/.

Cause

The outer loop in filesel_nav_last uses X as the cursor into LAST_GAME_DIR, but jsr fnl_enter_subdir clobbers X:

• fnl_cmp_subdir reuses X as its compare index (it only happens to leave it at testvar+2 on a successful match — that's incidental, not by contract);
• fnl_append_cwd uses X as the FILESEL_CWD write index;
• filesel_request_filelist calls WRAM_WAIT_MCU, hide_cursor, pop_window, none of which preserve X.

So the inx after fnl_enter_subdir increments whatever X ended up as — usually not the slash position the loop expects. The cursor drifts each iteration; whether the loop happens to terminate one component early depends on path content (which is why short paths sometimes appear to work).

The fnl_got_comp_eos branch is unaffected because it falls through to fnl_find_file/fnl_out and never re-reads from X.

Fix

 fnl_got_comp_slash:
   stx testvar+2           ; fnl_comp_end = x (exclusive, '/' position)
   jsr fnl_enter_subdir
   bcc fnl_out             ; not found — bail out
+  ldx testvar+2           ; restore x (clobbered inside fnl_enter_subdir)
   inx                     ; skip '/'
   bra fnl_comp_loop

Verified locally: with the patch the menu returns to the deepest folder for a 5-deep path. Haven't done an exhaustive sweep of Rom-mode edge cases.

[Xeroxxx]

@spend-cloud-tom Thanks for testing. The proposed fix is spot on.