Big Shoulders Stencil Text SC: correct override config source path for fontc_crater...

Big Shoulders Stencil Text SC: correct override config source path for fontc_crater build

The override config.yaml used `../`-prefixed paths that escape the repo
root when resolved by the build harness. Removed the `../` prefix (the source filename already matched the pinned commit).
Recipe output paths made repo-root-relative likewise.

Repo:   xotypeco/big_shoulders
Commit: 0b3d09a86862b19efae28eae0cd868f17c476b20 (unchanged; verified correct)
Config: ../Big-Shoulders... -> Big-Shoulders-Stencil/sources/BigShouldersStencil.glyphs (and recipe outputs)
Status: source path corrected (verified present at build commit; gftools-builder smoke-test passed)
Confidence: High

Assisted by an AI agent (Claude Opus 4.8)