fix(rsr-certifier): complete or honestly gate the uncompilable satellite

[hyperpolymath]

Problem

rhodium-standard-repositories/satellites/rsr-certifier is not currently a compilable Rust workspace. This was exposed while validating the security-only lock update in #688; it is independent of that update.

Exact reproduction

From the satellite root:

cargo check --workspace

The dependency graph first requires an explicit Git object-hash feature because the workspace declares:

gix = { version = "0.83", default-features = false }

With features = ["sha1"] temporarily added, compilation advances and exposes these source gaps:

• engine/src/adapters/mod.rs declares pub mod github;, but neither github.rs nor github/mod.rs exists;
• engine/src/db/cache.rs uses redis, but redis is undeclared;
• engine/src/db/documents.rs uses surrealdb, but surrealdb is undeclared;
• engine/src/db/graphs.rs uses arangors, but arangors is undeclared;
• engine/src/adapters/gitlab.rs names the parameter _payload but reads payload.

Required outcome

• decide and declare the supported Git object format feature explicitly;
• implement the GitHub adapter or remove the false module declaration;
• either declare and configure the three database backends or feature-gate unfinished adapters honestly;
• fix the GitLab parameter mismatch;
• make cargo check --locked --workspace and cargo test --locked --workspace real CI gates;
• add positive controls proving each enabled adapter is exercised, rather than treating scaffolding as implementation.

Do not add placeholder modules or empty adapter implementations merely to make compilation green.