Prepare for EigenScript's boolean type (EigenScript#1637)

[InauguralPhysicist]

Prepare for EigenScript's boolean type (EigenScript#1637)

Under EigenScript#1637 comparisons, file_exists and gfx_open return a
bool, and bool == num raises. Each site now tests truthiness, which
behaves identically on v0.44.0 (1/0) and on the bool-typed runtime.

• src/game.eigs:477,493 needs_retarget == 1 -> needs_retarget
  (bound to pred.wander_timer <= 0; every test died here)
• test_pacing.eigs:11 check helper ok == 1 -> ok (every caller
  passes a comparison)
• tidepool.eigs:147, test_gfx.eigs:4 result == 0 (gfx_open) -> not result
• src/game.eigs:1520, src/neural.eigs:513 file_exists of X == 0 -> not (file_exists of X)
• train.eigs:512,516 (file_exists of ..) == 1 -> (file_exists of ..)

Before: make test failed 4 of its checks on the bool binary (PR #1647,
79e800aa), at src/game.eigs:477 and test_pacing.eigs:11. After:
make lint and make test pass on v0.44.0 and on the bool binary with
byte-identical output. Launch witness (xvfb-run, tidepool.eigs): the
bool binary died at tidepool.eigs:147 before and now reaches the same
point v0.44.0 reaches.

Claude-Session: https://claude.ai/code/session_01KC99CmwatKssQYggkBCgwF

---

Prepares this repo for the boolean type in EigenScript#1637 (PR EigenScript#1647). Every edit is dual-compatible: this repo's real CI command was run on both the v0.44.0 release binary and the PR#1647 binary, with matching results except for the bump-phase golden items listed in EigenScript#1637's consumer report. This PR lands on the current v0.44.0 pin; the golden/C-API changes land with the later pin bump.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KC99CmwatKssQYggkBCgwF

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