PHLEGM v6 - FPS AlphaBlend compiler fix - 2026-10-02

Compiler run 2026-1002-2103-2252 failed all four Windows targets while building drawchr.lib.

Root cause:
- drawchr.bas used `Private Declare Function` for AlphaBlend. FreeBASIC does not allow Private/Public linkage modifiers on Declare lines.
- The two AlphaBlend invocations discarded a Function result using Sub-call syntax, producing the follow-on parser errors.

Fix:
- Reuse BLENDFUNCTION, AC_SRC_OVER, AC_SRC_ALPHA, AlphaBlend, WINBOOL, and msimg32 linkage from the existing windows.bi/wingdi.bi WinAPI declarations.
- Remove the duplicate private AlphaBlend declaration and duplicate blend structure.
- Consume both AlphaBlend return values with local WINBOOL variables.
- Preserve the requested FPS overlay: GUI CHR font, 3x scale, 80% opaque full green text on 50% opaque black, fixed three positions before the decimal and two digits after it.
- Preserve the cumulative NES vblank/deferred rendering and GUI machine/media/control fixes.

Validation:
- validate_fps_overlay.py now checks the WinAPI AlphaBlend integration and Function-call form.
- NES frame latch, FPS overlay, GUI command controls, CHR file/session, CHR remap, and installer-layout validators pass.
- Native FreeBASIC compilation still requires the Windows FBC environment.
