app: integrate backup diff restore into production TUI (M6.5)

[KeyffMS]

Implements M6.5.1 from #26: production integration of the existing #17 Backup / Diff / Restore core.

Scope:

• application-owned BackupRestore action/effect/view flow;
• complete backup capture through the existing BackupCoordinator and persisted storage;
• source backup load/validation and semantic diff;
• fresh pre-restore backup before plan construction;
• production RuntimeSessionControl restore contract wired to the existing WriteCoordinator;
• sequential restore continues to use the single guarded write authority, durable audit, trust, permit, exact confirmation and zero retry;
• real Backup / Diff / Restore TUI screen and keyboard flow instead of the placeholder;
• fail-closed coverage for missing audit/trust composition and production restore session sequencing.

Acceptance:

• rustfmt and workspace Clippy with -D warnings pass;
• feature-matrix checks, docs and architecture contract pass;
• staging/process/coverage quality gate passes on Debian 13 / Rust 1.97.1 / amd64 (vfd-lantern-podman-01);
• supply-chain checks pass;
• final immutable CI #1012 succeeded for exact head 5b314deb0233f71aab55c8f49cbcfc02f2cd98c9.

M6.5.1 is complete. M6.5.2 — full process-level PTY E2E Backup/Restore matrix — remains the next roadmap item.

Refs #25
Refs #26