Remove in-tree Cell and LTX crates after Cellule adoption

[forhappy]

The HTTP server already consumes Cellule at the pinned revision in Cargo.toml, but Crab still carried five duplicate Cell/LTX crates and built their qualification binary in release workflows. This removes those unused workspace packages and makes Crab invoke the qualification validator from the exact Cellule revision resolved by its locked dependency.

The server's Compose and protected-release evidence still bind the Crab source and image digest, compare all protected profiles against the pinned Cellule source, and fail if the locked revision differs from Cargo.toml. Legacy-only property, fuzz, and reference-Compose workflows move to Cellule PR #10. Historical architecture documents remain in Crab, with source links updated to Cellule.

Validation:

• cargo check -p crab-http-server --all-targets --locked and cargo build -p crab-http-server --locked passed with a per-worktree external target directory.
• Focused server test storage_root::tests::cellule_and_repository_stores_share_object_storage passed.
• The pinned Cellule qualification_receipt ran the profile command successfully; all 12 tracked profiles match the old Crab profiles byte for byte.
• Architecture gate tests and full architecture gate check, cargo fmt --all -- --check, actionlint on changed workflows, and git diff --check passed. UI build passed.

The protected provider/Kubernetes matrix and container-release workflow require their CI runners and image artifacts; those paths have not been exercised locally. Keep this PR draft until Cellule PR #10 and the relevant Crab CI checks pass.