Revamp login guards into general per-firm page guards

Replace the single hardcoded signed-out check with a guards list on each
firm: any guard can trip mid-run via a URL substring (checked on every
step) or a selector probe (checked when a step fails). Each guard defines
recovery steps or a human-wait fallback, a per-run trigger cap, and a
resume policy — 'continue' retries the tripped step, 'restart' rewinds
the run to step 1.

Runner bumped to 0.20.0; the server still ships the legacy
signedOut/authSteps shape for stale runners, and a new runner synthesizes
a guard from a legacy payload.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/db.ts

@@ -609,7 +609,7 @@ export const RUNNER_TIMEOUT_MS = 7000;
 /** The runner version this server's step vocabulary requires. A running process
  *  doesn't reload when the source changes, so an older one silently fails on
  *  steps it predates — the dashboard warns instead. */
-export const RUNNER_EXPECTED_VERSION = '0.19.0';
+export const RUNNER_EXPECTED_VERSION = '0.20.0';
 
 export interface RunnerHeartbeat {
     at: number;