chore(renovate): adopt the shared preset, drop the weekly window

[MarcelRoozekrans]

Blocked on ZeroAlloc-Net/.github#19. Until that preset is on main, github>ZeroAlloc-Net/.github will not resolve and Renovate will error on this repo. Merge #19 first.

Replaces this repo's weekly Renovate window with a three-day stabilisation period, and exempts security fixes from it.

What changes

   "extends": [
-    "config:recommended"
+    "config:recommended",
+    "github>ZeroAlloc-Net/.github"
   ],
-  "schedule": ["before 6am on monday"],
-  "timezone": "Europe/Amsterdam",

The schedule has to be deleted here rather than in the preset — repo config wins over a preset, so leaving it would keep the Monday window in force and negate the change entirely. timezone goes with it, since it only ever affected schedule.

Why

The window was doing two jobs: batching updates, and letting a release sit long enough to be found broken. The preset keeps the second via minimumReleaseAge: "3 days" and drops the batching — an update published on Tuesday now arrives Friday instead of waiting for the following Monday.

More importantly, security updates inherited that schedule. ZeroAlloc.Serialisation had MessagePack 3.1.8 parked under Awaiting Schedule on its dependency dashboard while 3.1.4 carried fourteen advisories, three high severity — with audit-as-error making main unbuildable for two months, unnoticed because CI only runs on push and pull_request.

Under the preset, security fixes bypass both the wait and any schedule, and are raised as fix(deps) so release-please actually ships them. As chore they would merge to main and leave the published package vulnerable.

Note

Routine update cadence is otherwise unchanged; any packageRules, grouping and automerge settings in this repo are untouched.