Add SQLite IOERR correlation diagnostics

[callumalpass]

Summary

• preserve SQLite primary and extended result codes for local registry failures
• correlate relay inventory failures with the exact registry phase
• add privacy-safe structured fields to notification recovery and relay sync warnings

Verification

• cargo fmt --all -- --check
• cargo test -p mdbase-connect-core (125 passed)
• cargo test -p mdbase-connect-daemon (54 passed)
• cargo clippy -p mdbase-connect-core -p mdbase-connect-daemon --all-targets -- -D warnings
• cargo check -p mdbase-connect-core -p mdbase-connect-daemon --all-targets

A subsequent full-workspace aggregation was interrupted while linking unrelated AWS/hosted-provider targets because the workstation filesystem reached its existing capacity ceiling; the exact disposable Cargo target cache was cleaned. CI should provide the authoritative full-workspace result.

Staging follow-up only. Do not promote production as part of this PR.