db-mode config changes apply live in-process

settings and upstream writes now follow a prepare, commit, publish, retire
contract: candidates are built and validated before the database transaction,
published as infallible pointer swaps, and old generations retire after their
readers drain. per-query policy values snapshot once per query; upstream pool,
cache, rate limiter, sessions, api limiter, log sink, blocklist scheduler and
the query-log queue each gained one named live operation. restart_required
shrinks from every scalar key to the bind keys and web.enabled; the admin ui
drops its restart notices for everything else. file mode is unchanged.

CHANGELOG.md

@@ -8,6 +8,7 @@ Sections are written by hand. Nothing here is generated from commit messages: th
 
 ### Changed
 
+- **Almost every settings change now applies while the server runs.** When the database owns the configuration, saving a setting takes effect immediately — the blocking response, upstream timeouts, cache size, rate limits, session lifetime, log level and destination, blocklist update schedule, privacy flags, disk thresholds and the query-log buffer all reconfigure the running process, exactly as Pi-hole and AdGuard Home do. Nothing is written to the database unless the running server already accepted it, so the API can never report a value the process refused. The restart-required set shrinks from every scalar key to the twelve that genuinely need one: listen addresses and ports, and turning the admin interface itself on or off. The admin pages drop their restart notices for everything else, and an upstream edit — the loudest offender — now applies to the next query. A configuration file still works the way it always has: edit the file, restart the process.
 - **The release cut refuses to ship an undisclosed query-log schema change.** `zig build cut` now compares the `querylog.db` schema fingerprint of the previous release tag against this tree's, and when they differ it requires the changelog section for the version being cut to state that the upgrade discards the stored query history. 0.0.9 changed the schema and its announcement did not mention it; the file is never migrated, so that upgrade silently threw every logged query away.
 
 ## [0.0.9] - 2026-08-22