Scale Cell write admission and batch durable root coverage

[forhappy]

Independent Cells reserved a maximum-sized transaction allowance, which refused otherwise-small concurrent writes. Admit SQLite database, WAL, SHM and temporary-file growth before I/O, and reserve capture/commit credit from the database image bound. Preserve resource causes after proved rollback so the same owner and request identity can retry. Ambiguous commits and capture failures still fence.

Batch exact node-authority coverage across independent and coalesced Cell roots, preserving durability bindings, sparse completion history, cancellation and retirement. Keep a follower-proven owner usable after a later pre-SQL capacity refusal.

Use the installed node lease for quiet Cell liveness, removing periodic per-Cell control writes. Long preparation still checks the shared monotonic lease; exact-root publication, expiry fencing and unleased renewal behavior remain intact.

Add an offered-load Axum driver and application-owned follower fixture with pinned mTLS and canonical fsynced stores. Audit original identities and scoped receipts after cold restore. Critical measurements and source/binary provenance live in crates/cellule-axum/performance; capacity qualification remains open.

Validation: isolated LTX tests with and without replica features, runtime library, full runtime integration and durability tests, strict LTX/runtime/Axum Clippy, and default release builds pass. Format, layer/layout, documentation and SQL/peer checks pass. Broad workspace and process checks run in CI. The object/follower qualification gates are unchanged; current broad CI runs against the updated source.