browserrot: Phase A-tier-1 site-side rotation engine (go-rod)

Deterministic, headless browser-driven password rotation:
discover change page via RFC 8615 / links, inject old+new over CDP
(no model in the loop), submit, and re-login to verify the new
password before commit. Implements rotate.Rotator so the mandatory
backup gate, verify-before-revoke ordering, and proof gate apply
unchanged; RevokeOld is a no-op (the site invalidates the old pw).

Proof-as-data per Site: the engine is LIVE-VM (real headless
Chromium vs a real local change-password form, via
lab-provision-browserrot.sh / TestIntegration_realBrowserRotation);
real-site selector tables stay UNPROVEN and nothing auto-registers
into production rotate yet. 14 packages, -race clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

go.mod

@@ -22,6 +22,7 @@ require (
 	github.com/charmbracelet/x/cellbuf v0.0.13-0.20250311204145-2c3ea96c31dd // indirect
 	github.com/charmbracelet/x/term v0.2.1 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
+	github.com/go-rod/rod v0.116.2 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
@@ -33,6 +34,11 @@ require (
 	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
+	github.com/ysmood/fetchup v0.2.3 // indirect
+	github.com/ysmood/goob v0.4.0 // indirect
+	github.com/ysmood/got v0.40.0 // indirect
+	github.com/ysmood/gson v0.7.3 // indirect
+	github.com/ysmood/leakless v0.9.0 // indirect
 	golang.org/x/sys v0.46.0 // indirect
 	golang.org/x/text v0.31.0 // indirect
 )