fix: fail incomplete database inspections

[DivyamTalwar]

What and why

Closes #98.

When at least one database succeeded, runInspectAll calculated its exit status only from successful contexts, ignoring a failed database. Preserve the successful subset of the report, but let execution failure (exit 3) take precedence over finding thresholds. The all-failed and complete-success cases retain their existing behavior.

Verification

Verified commit: 945e9a67b93b56a90cdc81ec59cf9cf84366dcbb.

• The actual main/Cobra subprocess regression fails on the base behavior: partial clean inspections exit 0 and partial critical inspections exit 2 rather than 3. Only discovery/collection are injected; CLI parsing, fanout, rendering and process exit remain real.
• Affected command race tests, clean committed-HEAD bash scripts/gate.sh, and go test -race ./... pass.
• Controls cover complete clean/warn/critical results, fail-on none and critical, partial failures, all failures, retained JSON output and skip diagnostics.

Scope, risk and rollback

No collector SQL, model fields, dependencies or migrations change. PR #38 overlaps the fanout file but its partial-failure handling is conditional on all-instances; this corrects plain all-databases independently. No live connection-failure simulation is claimed. Revert this commit to restore the former exit precedence.

Checklist

• scripts/gate.sh passes on committed HEAD; full race suite passes.
• Read-only, privacy and deterministic-finding invariants preserved.
• No new finding or model.Context JSON field; catalog/model schema unchanged.