fix: remove automergeType branch, incompatible with required status checks

Branch automerge creates branches without PRs, so the lint workflow's
pull_request trigger never fires. Required status checks stay pending
forever, blocking automerge. Reverting to PR-based automerge which
triggers lint via pull_request and satisfies branch protection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: owine

.github/renovate.json

@@ -7,7 +7,6 @@
   "timezone": "America/Chicago",
   "prHourlyLimit": 0,
   "prConcurrentLimit": 0,
-  "automergeType": "branch",
   "commitMessageTopic": "{{depName}}",
   "commitMessageExtra": "{{#if isDigest}}digest to {{newDigestShort}}{{else}}to {{#if isMajor}}{{prettyNewMajor}}{{else}}{{prettyNewVersion}}{{/if}}{{/if}}",
   "vulnerabilityAlerts": {

default.json

@@ -8,7 +8,6 @@
   "timezone": "America/Chicago",
   "prHourlyLimit": 0,
   "prConcurrentLimit": 0,
-  "automergeType": "branch",
   "commitMessageTopic": "{{depName}}",
   "commitMessageExtra": "{{#if isDigest}}digest to {{newDigestShort}}{{else}}to {{#if isMajor}}{{prettyNewMajor}}{{else}}{{prettyNewVersion}}{{/if}}{{/if}}",
   "vulnerabilityAlerts": {