PHLEGM v8 checkpoint 61: Windows GUI icon forward-declaration compile fix

Baseline: PHLEGM v8 Developer Distribution SNES Slot Icons checkpoint 60.
Reported failure: PHLEGM-v8-Compiler-Logs-2026-1010-1656-1171.zip.

Diagnosis:
- All four Windows 32/64 OpenGL/D3D11 configurations stopped compiling
  at src/lib/gui_windows.bi(892) error 42: variable not declared,
  GuiIconKindForItem.
- GuiIconRefresh() called GuiIconKindForItem() before the function's
  definition at line 961. FreeBASIC requires a forward declaration.

Fix:
- Added Declare Function GuiIconKindForItem(ByVal itemOrdinal As Integer)
  As Integer alongside the existing GuiIconArchiveBadges declaration.
- Function implementation and all other source/cfg/data/tooling unchanged.
- Checkpoint 60 SNES support-slot diagnostics, per-kind cached icons, and
  conditional ZIP mini-folder/cartridge cutouts are preserved.
- Source .bi file retains CRLF line endings.

Validation:
- Confirmed log reports same unresolved-function compiler failure for all
  four Windows targets.
- Verified function declaration now precedes the call, and definition
  continues to match its signature.
- SHA-256 comparison with checkpoint 60: only gui_windows.bi (plus this new
  documentation note) differs inside PHLEGM v8 source tree.
- ZIP CRC/integrity and checksum file checked after packaging.
- Native FreeBASIC build not available in this environment; run full Windows
  target build matrix using existing bootstrap to confirm success.
- Compiler progress history remains undisturbed by the failed build.
