Add additive TILT billboard masking API

[Nexhas28]

Summary

• add an optional additive render_pipelines.drawBillboards(ctx) stage inside built-in TILT
• expose a read-only semantic collision-map view plus cached map cutout, source-mask, and billboard queue helpers
• integrate source masking and Y-sorted upright cards across Gen 1, Gold, Silver, and Crystal
• preserve nearby terrain when removing the flat source silhouette, preventing duplicate flat/upright structures

This is a presentation-only API. It does not change collision, movement, warps, scripts, saves, battles, or link behavior.

API

During built-in TILT, an enabled pipeline may implement drawBillboards(ctx). The context provides:

• ctx.map: semantic map dimensions and collision-derived cell(x, y) flags
• ctx.drawMapCutout(...): draw a cached alpha card for a seeded map component
• ctx.maskMapCutout(...): remove that same component from the active ground canvas
• ctx.billboard(worldX, worldY, drawFn): merge the card into the normal upright-object Y-sort
• ctx.mapScale: map-pixel to world-pixel scale

maskMapCutout returns false when the region cannot be masked safely, allowing mods to skip the corresponding upright card and avoid partial rendering.

Verification

• luajit tests/mod_render_tests.lua — 62/62
• additive billboard/cutout suites — 59/59
• changed Lua modules compile with luajit -b
• luajit tests/run_engine.lua — 367/368 in the restricted workspace; the sole failure was temporary-fixture write permission
• luajit tests/engine/required_import_streaming_test.lua — 11/11 when rerun with repository write access
• python3 tools/modkit.py docs
• git diff --check

Opened as a draft for API and renderer review.

[bryanthaboi]

5 million files changed