Merge pull request #288 from AdaWorldAPI/claude/drop-burn-submodule

build: drop the reference-only burn submodule that broke every git-dep consumer

Author: AdaWorldAPI

.gitmodules

@@ -0,0 +1,22 @@
+# Upstream provenance — where the reference tree went
+
+`crates/burn/upstream` was a git SUBMODULE pointing at
+`https://github.com/AdaWorldAPI/burn.git` (last gitlink
+`9b2b67127b0fbb5387021faf540b7b12b9c4e943` = that repo's merge of PR #4;
+upstream lineage: tracel-ai/burn, `v0.21.0-pre.2`). It was pure reference
+material: `crates/burn/src` reads nothing from it, and `crates/burn` is
+workspace-EXCLUDED besides.
+
+It is gone because a reference-only submodule taxes EVERY consumer of this
+repo as a git dependency: cargo clones git deps with submodules
+unconditionally, so `medcare-rs`'s Railway build fetched the full burn fork
+just to compile `chacha20` out of this repo — and on 2026-08-31 that fetch
+died on GitHub's unauthenticated shared-IP rate limiting
+("could not read Username", after three spurious-network retries), taking
+the deploy down. A gitlink is also a commit-pin on an internal sibling —
+the consumer pin law's spirit, one layer down.
+
+Need the reference tree? Clone the sibling directly:
+`git clone https://github.com/AdaWorldAPI/burn.git` — the fork repo is the
+address; this file is the provenance record (tags over pins, per the
+internal-pin prohibition).