merge(main): integrate published v0.7.0 and runtime safeguards with diagnostics history

Bring the 14 remote main commits into the local canonical line after preserving the schema-diagnostics side branch. The merge-tree preflight was conflict-free and the remote range contained no deleted or renamed tracked paths. This carries the published v0.7.0 release record, prepared-SQL/WAL recovery safeguards, review-threshold and sync collision fixes, and their tests while retaining the already equivalent runtime index diagnostics.

Validation: merge-tree produced a clean tree, git diff --check and rustfmt on the resolved diagnostic files passed. Cargo validation remains unavailable because sbh check --need 20G reports critical disk pressure (2.47 percent free).