v0.4.0

Adds the OSD disc-image browser and fixes VF2 input lag, plus an M13 A1
timing-accuracy refinement and a documentation overhaul. Backwards-compatible:
the save-state format (v9) and the bios_boot golden hash are both unchanged,
so existing save states still load.

Added

• Disc-image browser in the OSD. Esc → Load Disc… opens a filesystem
  browser: navigate directories and pick a .cue / .iso / .ccd; selecting
  an image loads it and power-cycles to boot the game. The menu stays core-free
  and fs-free (the frontend supplies the directory listing); a scrolling
  viewport handles large directories.
• Raster batch-drain jitter probe (M13 A1, dev instrumentation) — an
  observer-only check confirming VCNT/TVSTAT reads are never stale, the evidence
  that the HBlank clamp edge can stay deferred.

Changed

• SMPC command dispatch is now an exact mid-batch event (M13 A1). A queued
  command breaks the scheduler batch so it dispatches within one instruction of
  the COMREG write, matching the LLE reference. Golden-safe — a timing-fidelity
  improvement, not a behaviour regression.
• Documentation overhaul. Normalised all roadmap tables to one format;
  consolidated Tier G (residual reference-audit items) with status markers;
  retired the point-in-time MAME/Mednafen cross-reference audits, folding their
  durable residue into bootstrapping.md §C.1 and roadmap Tier G; added an
  Enhancements section (EN1: GLSL shader presets); and synced the disc
  browser into the feature docs.

Fixed

• Input lag / "not steady 60 fps" in VF2. The emu-thread frame pacer was
  chronically collapsing ~1/3 of rendered frames ("run 2, show 1") because it
  chased an audio-reserve target it structurally couldn't reach. It now renders
  every game-frame in normal play, collapsing only when the audio reserve
  has genuinely drained toward an under-run — smoother motion and lower input
  latency. The SAT_MAX_BURST env var becomes the catch-up ceiling (default 2;
  =1 disables catch-up).