docs: explain why libsqlite3-sys is pinned to 0.35 in server/Cargo.toml

The dep is declared only to flip on the `bundled` feature for the
static musl build, and 0.35 is the ceiling forced by rusqlite 0.37
(matrix-sdk-sqlite) and sqlx-sqlite 0.9.0-alpha.1. Future readers
no longer have to reconstruct that from cargo-tree.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/Cargo.toml

@@ -36,7 +36,14 @@ pulldown-cmark = { workspace = true }
 regex = { workspace = true }
 tokio-tungstenite = { workspace = true }
 
-# Force bundled SQLite so static musl builds don't need a system libsqlite3
+# Listed here to enable the `bundled` feature, which propagates via Cargo's
+# feature unification to sqlx-sqlite and matrix-sdk-sqlite (rusqlite) so the
+# static musl docker build can compile SQLite from source instead of linking
+# against a missing system libsqlite3.
+#
+# The 0.35 pin is the ceiling: rusqlite 0.37 (matrix-sdk-sqlite) requires
+# 0.35.x exactly, and sqlx-sqlite 0.9.0-alpha.1 requires >=0.30, <0.36. Bumping
+# this needs one of those upstreams to widen their range first.
 libsqlite3-sys = { version = "0.35.0", features = ["bundled"] }
 sqlx = { workspace = true }
 wait-timeout = "0.2.1"