ci: drop the renovate rebase dispatch

[BryanFRD]

Renovate now runs as a CronJob in the cluster (FerrLabs/Infra#424), and FerrLabs/.github#339 removes renovate.yml and reusable-renovate-dispatch.yml. The "rebase now" dispatch has nothing left to trigger: a ticked checkbox is handled by the next in-cluster run (every 2 h).

Merge after FerrLabs/.github#339.

[ferrfleet]

Clean deletion. Nothing else in the repo references renovate-rebase.yml or reusable-renovate-dispatch.yml, and renovate.json only extends the org preset, so it is unaffected. The merge-order note is a safety margin rather than a requirement: the uses: line pins the reusable workflow by SHA, so it would keep resolving even if FerrLabs/.github#339 lands first.

Nit (outside this diff, but the same migration): .github/workflows/ci.yml gates the advisory cargo vet path on github.event.pull_request.user.login == 'ferrlabs-renovate[bot]'. If the in-cluster CronJob authenticates as anything other than that same App, the condition stops matching and lockfile-only PRs get the hard vet gate back. That fails closed, so it is not a security problem, just weekly noise on a required check. Worth confirming the cluster Renovate uses the same App credentials.

[github-actions]

SonarQube — aucune nouvelle issue

_{Comparaison entre le projet bac à sable de cette PR et la branche par défaut : SonarQube Community n'analyse pas les PR, ce delta est calculé côté CI. Détail}

[BryanFRD]

On the cargo vet gate: the in-cluster Renovate authenticates as the same GitHub App and sets the same author (ferrlabs-renovate[bot], FerrLabs/Infra#424), so the login check in ci.yml keeps matching.