setdb: connect by db-name (cross-server search) + live --status health

[sibinc]

Builds on and supersedes #25 (its docs/skill commits are included here).

New capabilities

Connect by db name — setdb <dbname>. If the first arg isn't a known server id, it's treated as a database name: setdb searches every server in the group, finds which one hosts it, ensures the connection, and sets the active db. Unique → auto; multiple → prompt (JSON: error listing them); none → error. Example: setdb test_sfchyd2906.

Live --status health check. setdb --status now pings the current connection and reports ● connected (301ms) / ○ DOWN — <error> (JSON: connection: {ok, ms}). Enabled by stamping the source connection id into active-db.php as a PHP comment (// setdb server=<id>), which parseActiveDb reads back. --no-check skips the ping.

Interactive db listing. With a server chosen but no db given, setdb lists the server's databases (with a filter prompt) to pick from, instead of blind-typing.

Connection ensured before set. A ping runs before writing active-db.php (skipped with --no-verify), so a set never points the app at an unreachable server.

Standalone lookups unchanged and documented: lwdb servers, lwdb dbs <server> [pattern], lwdb find-table.

Also included (from #25)

• docs/setdb.md step-3 fix (web-root .lwdb, not home dir).
• lwdb skill: new setdb section + activation trigger.

Tests

13/13 pass (added server-stamp round-trip). Manually verified: db-name search → set, --status health, stamped active-db.php lints + app connects.