docs: remove volatile corpus counts

[Teakowa]

Summary

• remove hard-coded corpus inventory counts from durable real-project evidence documentation
• retain provenance-oriented descriptions for source repositories, revisions, digests, and fixture paths
• leave corpus membership, fixtures, tests, and CI behavior unchanged

Verification

• cargo fmt --all --check
• cargo run --locked -p workshop-rs --bin workshop-catalog-gen -- check
• cargo test --workspace --all-targets
• git diff --check

Fixes #104