feat(disk): High-fidelity Disk II emulation with .woz support

[relmer]

Summary

Implement accurate Disk II hardware emulation to support copy-protected software and match real hardware behavior. Currently the Disk II controller uses a simplified digital model that works for standard DOS 3.3 and ProDOS disks but fails on software that relies on analog timing, half-tracks, or bit-level disk access.

Current Limitations

• No spin-up delay — motor reaches speed instantly; real hardware takes ~70ms
• No rotational position tracking — reads return the next sequential nibble regardless of timing; real disk spins continuously and read position depends on CPU cycle count
• Simplified stepper motor — single-step quarter-track increments only; real hardware supports half-track positioning from dual-phase magnet interactions
• Motor state doesn't gate reads — data is returned even when motor is off; real hardware returns garbage until motor is up to speed
• No write support through nibble path — only sector-level writes exist via WriteSector
• .dsk only — sector-level images discard all timing, sync, and raw flux data

Proposed Implementation

Phase 1: Timing and Motor Accuracy

• Track motor state with spin-up/spin-down timing (~1 revolution to reach speed)
• Implement rotational position based on CPU cycle count (nibble stream position = total cycles modulo track length in cycles)
• Gate data reads on motor-running state (return random/zero when motor is off or spinning up)

Phase 2: Half-Track and Stepper Fidelity

• Model dual-phase magnet interactions for half-track positioning
• Support head positioning at any quarter-track (0-139), not just whole tracks
• Return appropriate data when head is between tracks (noise, partial reads, or half-track data if available)

Phase 3: .woz Disk Image Support

• Parse WOZ 1.0 and WOZ 2.0 file formats (bit stream per track, timing metadata)
• Support half-track data stored in .woz images
• Implement bit-level read/write using the raw flux stream instead of pre-nibblized sectors
• Preserve sync gaps, weak bits, and timing variations that copy protection relies on

Phase 4: Write Path

• Implement bit-level write through the shift register and data latch (Q6/Q7 state machine)
• Write nibble data back to the track buffer
• Support write-back to .woz images (and optionally .dsk with re-encoding)

Reference

• AppleWin Disk II implementation — implements spin-up, rotational position, half-tracks, and .woz support with ~99% copy protection fidelity
• WOZ Disk Image Reference — technical specification for the .woz format
• Understanding the Apple II Disk II — hardware-level explanation of stepper, motor, and data path

Acceptance Criteria

• Motor spin-up delay prevents reads for ~70ms after motor-on
• Rotational position is cycle-accurate (read position depends on when the read occurs)
• Half-track stepping works with dual-phase magnets
• .woz 2.0 images load and boot correctly
• At least 3 known copy-protected titles boot successfully from .woz images
• Standard .dsk images continue to work (backward compatible)