Delete dead workflows

Dependabot config copied from upstream; upstream CI in a copy we do not
release from.

Claude-Session: https://claude.ai/code/session_01HuMDfgFssPUptYUzgZ6Cp8

.github/dependabot.yaml

@@ -1,148 +0,0 @@
-# Test-level dependencies: the older the better. Inhibit dependabot, so we only accept manual updates.
-version: 2
-updates:
-  # Disable Dependabot for ci/docker (all ecosystems)
-  - package-ecosystem: "docker"
-    directory: "/ci/docker"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "pip"
-    directory: "/ci/docker"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "npm"
-    directory: "/ci/docker"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "github-actions"
-    directory: "/ci/docker"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  # Disable Dependabot for tests/integration (all ecosystems)
-  - package-ecosystem: "docker"
-    directory: "/tests/integration"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "pip"
-    directory: "/tests/integration"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "npm"
-    directory: "/tests/integration"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "github-actions"
-    directory: "/tests/integration"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  # Disable Dependabot for docker/test (all ecosystems)
-  - package-ecosystem: "docker"
-    directory: "/docker/test"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "pip"
-    directory: "/docker/test"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "npm"
-    directory: "/docker/test"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "github-actions"
-    directory: "/docker/test"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  # Disable Dependabot for all Rust (cargo) dependencies.
-  # Rust crates are pinned via Cargo.lock and built reproducibly; updates must be
-  # done manually together with lockfile and vendored-source refreshes.
-  - package-ecosystem: "cargo"
-    directory: "/rust/chcache"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"
-
-  - package-ecosystem: "cargo"
-    directory: "/rust/workspace"
-    schedule:
-      interval: "monthly"
-    cooldown:
-      default-days: 90
-    open-pull-requests-limit: 0
-    ignore:
-      - dependency-name: "*"