Flip push/register from 0.1 → 0.2 (after gateway #8 merges)

[stormer78]

Summary

The plugin currently sends push/register as 0.1 because the push gateway
only accepted 0.1. The gateway now dual-accepts 0.1 and 0.2, so the plugin
can migrate push/register to 0.2 and finish moving its VTA-facing tasks
off the deprecated 0.1 version.

Blocked on

• Accept push/register/0.2, update deps, and remove the rsa (Marvin Attack) dependency vti-push-gateway#8 (closes Add push/register/0.2 handler (Trust-Tasks 0.2 migration) vti-push-gateway#7) — adds the
  push/register/0.2 handler. Flip only after that PR merges and is
  deployed.

Context

push/register was the last task pinned to 0.1: its payload has no
enum-valued fields (registration + controllerVtaDid), so 0.1 and 0.2 are
field-identical and this is effectively a version-string bump. The gateway
returns push/register/0.2#response with payload.wakeHandle = {gateway, handle} for a 0.2 request, and keeps 0.1 working, so the change is safe to
ship independently of the gateway rollout timing (0.1 stays valid until the
flip).

This was tracked alongside the original web-push wake wiring work (the
feat/web-push-wake-wiring branch).

What to do

• Change the push/register request type from
  https://trusttasks.org/spec/push/register/0.1 to …/0.2.
• No payload field changes are required (schemas are identical).
• On the error path, expect trust-task-error/0.2 (lowerCamelCase codes) — the
  gateway now emits 0.2 framework errors uniformly.

Acceptance

• Plugin registers via push/register/0.2 and receives a
  push/register/0.2#response with a usable wakeHandle.
• No remaining references to push/register/0.1 in the plugin.