fix(indexer): bump Dockerfile Deno to 2.7.12 to match local lockfile
deno.lock locally is generated by Deno 2.7.x (lockfile schema v5).
The container was pinned to 2.1.4, which fails to read v5 lockfiles
('Unsupported lockfile version 5'). Pin the image to 2.7.12 so the
build container matches the local toolchain that produced the lock.
Made-with: Cursor