Fix personal WP Health Check recovery boot

[akirk]

What changed

• Mark Health Check recovery URLs with an explicit ?playground-recovery-mode=health-check query param. → This also will allow us in support cases to just send the URL https://my.wordpress.net/?playground-recovery-mode=health-check to a user
• Detect that marker before boot probes WordPress, so recovery mode skips the pre-blueprint wp-load.php path that can crash on broken active plugins.
• Remove the recovery marker from the URL after the blueprint is consumed.
• Add coverage for recovery URL generation and router cleanup.

Why

The previous recovery flow inferred recovery mode from the decoded blueprint landing page. Personal WP could still run the WordPress install check before recovery setup, and that check loads wp-load.php. If an active plugin fatals there, Health Check never gets installed.

Testing

• NX_ISOLATE_PLUGINS=false NX_DAEMON=false npm_config_cache=/tmp/npm-cache npm_config_update_notifier=false npm exec --offline -- nx test playground-personal-wp
• NX_ISOLATE_PLUGINS=false NX_DAEMON=false npm_config_cache=/tmp/npm-cache npm_config_update_notifier=false npm exec --offline -- nx run playground-personal-wp:typecheck
• NX_ISOLATE_PLUGINS=false NX_DAEMON=false npm_config_cache=/tmp/npm-cache npm_config_update_notifier=false npm exec --offline -- nx run playground-personal-wp:lint