fix(renovate): run lock file maintenance weekly, not daily

Lock file maintenance runs every morning because the runner forces schedule: null, and Renovate reapplies force after it merges lockFileMaintenance. The lock file MR automerges minutes after Renovate rebases every other branch, so each open npm MR conflicts again the same day. On gitlab-com/public-sector/exhibits/tenet that happened on 20 days between 2026-09-02 and 2026-10-06.

sequenceDiagram
    participant R as Renovate, 06:00 UTC
    participant N as npm MR
    participant L as Lock file MR
    participant M as main
    loop every day
        R->>N: rebase onto main
        R->>L: refresh package-lock.json, last branch
        L->>M: automerge when the pipeline passes, about 06:20
        M-->>N: package-lock.json conflict until the next run
    end

This MR:

• forces only automergeSchedule and prHourlyLimit in .gitlab-ci.yml
• gives lock file maintenance before 9am on Sunday in renovate-config.json
• drops the preset's top-level Monday window, which the force always nulled

Every other update still runs daily. A project outside this group that extends the preset without forcing a schedule goes from a Monday window to daily updates; the CHANGELOG says so. A dry run on gitlab-com/public-sector/exhibits/tenet and gitlab-com/public-sector/reference processes the typescript branches and skips lock file maintenance as not within schedule.