RetroRecomp v1.2.3 — longer discovery routes on Mega Drive and Super Nintendo

RetroRecomp v1.2.3 — longer discovery routes on Mega Drive and Super Nintendo

• Advanced 16-bit scan. The Advanced Mega Drive scan option becomes the
  Advanced 16-bit scan and now applies to Super Nintendo cartridges too. On
  both consoles it runs the attract sequence for 24,000 frames and adds two
  reproducible pseudo-random play routes of 18,000 frames each: long
  movement phases that often hold a button, short taps, paired Start presses
  that pause and resume, occasional Select and player-two input, and neutral
  pauses between phases. The routes are ordinary controller input seeded from
  the exact ROM, so every conversion of the same cartridge replays the same
  routes and the reference run receives the same script; the report records
  each route's seed and index. Mega Drive keeps its authored varied-input,
  early-start and menu replays. Measured with an empty library on Donkey Kong
  Country, the routes exercised 59 SPC700 opcode variants that the existing
  scenarios did not reach; on Sonic the Hedgehog they added one Z80 driver
  image. Neither game reached a later level this way, so the option broadens
  the tested first-level paths rather than exploring whole games.
• Documentation index and link check. docs/INDEX.md lists every public
  document by theme, and tools/check_doc_links.py verifies the relative links
  of the documentation; it runs in the test suite.

The generated games do not change: regenerating is not needed, and quick
states, settings, libraries and cartridge saves are unaffected. Because the
16-bit compiler code changed, the converter may report Mega Drive and Super
Nintendo games as made by an earlier converter; regenerating them produces the
same executables. With the option enabled, a conversion takes about eight times
longer than the standard scan (16 minutes for Sonic the Hedgehog on the test
machine). The option stays off by default.
Linux remains qualified on Debian 13 / glibc 2.41; other baselines need testing.