Sonic 3 family v0.7.4

This Sonic 3-family bugfix update addresses 25 report groups. Another 17 groups have explicit original-behavior, nonreproduction or deferred decisions; those are not counted as fixes.

• Restore the full Blue Spheres field in standalone Sonic 3 by reading its native board address. Standalone S&K's actual special stage was separately checked and works.
• Keep the visible Hydrocity tunnel's colors until it leaves the wide view, and repair the current's missing edge fill and surface strips.
• Correct Angel Island and Hydrocity art, map and title-card handovers in the extended view; retain revealed hollow trunks and coherent level-select lettering.
• Restore the original interrupt bookmark during Angel Island's bombing transition. The redraw now takes 8 wall frames instead of 32 in both Sonic 3 and S3&K. Variable loading time still differs with widescreen headroom; exact cycle parity is not claimed.
• Repair the HCZ act-transition splash-slot conflict and discover the original camera-sabotage continuation handlers in both hosts.
• Restore bright Competition/Special Stage backgrounds and correct standalone S&K title/Mushroom Hill intro art publication.
• Accept the specifically verified Sega Classics Steam S3&K image without modifying its bytes. Unqualified variants remain subject to the normal ROM checks.

Fresh packages default to adaptive Fit widescreen and diagnostics. Explicit saved choices and native saves are preserved. The included diagnostic replay helper supports current-build captures; old save states remain build-specific. Disk saves retain the existing frame-loop restart limitation and do not promise immediate uninterrupted phase parity.

No ROM or converted stage bank is included. Use your own supported game image.

Qualified source candidate: game d0c6bfa7891cb34d741ba589e571b14ac1074a4a, engine 3ebf1fc50e0bb665f0378bdae6f2e7be31a5ad61, UI aee41e1dc834c105fd290d7c833bbbd7fbc71c1e. Detailed per-report evidence and bounded deferrals are retained in the project feedback ledger.