v0.7.5: optional legacy cartridge generation

• Add explicit --legacy-cart compatibility output for objects, scenes, demo menus, HiFi, Demo Cart 2, colour tests and cartridge smoke tests. Standard generation remains the default; no automatic fallback occurs.
• Restore the preserved pre-0.7.4 boot programs and original scene ROMH packing together. Legacy mode omits EAPI/EF-Name and does not relocate the scene's 1 KiB into bank 2 ROML.
• Warn that the selected method was discontinued since 0.7.4 and may fall outside recommended EasyFlash layout conventions. Retain physical capacity, packet and reset-vector checks.
• Label automatically named compatibility outputs with -legacy and record cart_write_method in manifests. Keep these outputs out of the current release index.
• Correct the default object/scene bootstraps to initialize the CPU port latch $01 before direction register $00, matching the EasyFlash guide. Historical boot files remain unchanged.
• Verify exact legacy reproduction against the downloaded v0.7.3 release: all 20 control CRTs have equal before/after SHA-256 and zero differing bytes, including headers, with no masking or binary patching. Controls use the published identities, including 0.7.2 for inherited Marbles/HiFi; actual release builds use 0.7.5.
• Rebuild current examples and refresh release validation. See 0.7.5 release notes.