refactor(settings): the boot config provider reads through StationSettingsRepository (gh-#406 slice 5)

[genwave-radio]

gh-#406 L2 burn-down, slice 5 of 5 — stacked on slice 4 (merge in order; merge commits, not squash). Merging this completes the issue: the L2 baseline is down to the two designed composition-root exemptions, zero debt rows.

⚖️ The "needs a design" entry, resolved as scoped: the law is about where Npgsql lives, not how the caller is built. StationSettingsConfigurationProvider.Load() (sync, pre-DI, the IConfigurationProvider contract) now constructs new StationSettingsRepository(connectionString) itself — the exact boot path slice 3's plain-string ctor was designed for — and calls the new sync ReadAllForBoot() (SQL byte-identical, documented as the deliberate sync exception). using Npgsql gone; the NpgsqlException catch becomes DbException (same translation slice 3 documented — identical failures caught, cancellation still propagates).

🛡️ Boot posture byte-identical: empty-connection-string short-circuit, allowlist filtering, scalar/array expansion, and catch-log-continue-with-empty-overlay all untouched — only the row fetch moved. Field check after deploy: the config boot echo in Loki should read exactly as before.

📉 Baseline: last debt row deleted; ExemptionBaseline's header rewritten to the end state (two designed rows, the five debt rows recorded as burned down via gh-#406, "not on this list still fails" retained).

✅ At this tip: build 0 warnings; Architecture 104/104 (L2 sees only the designed exemptions); MediaLibrary 769/769 full; Host settings-filtered 167/167 + seed-filtered 37/37.