Integrate renovate bot for all dependency updates (#37050)

Replaces Dependabot with Renovate. The new setup:

- One PR per ecosystem (GitHub Actions, Go modules + Makefile go-tool
pins, npm, Python via uv, Nix flake), opened weekly on Mondays with a
5-day release-age cooldown. Vulnerability PRs ship next-day via daily
cron + Renovate's `vulnerabilityAlerts` schedule bypass.
- All `uses:` action refs SHA-pinned with patch-level version comments
(same format as #36971, which this supersedes);
`helpers:pinGitHubActionDigests` keeps future bumps in that format.
- `renovatebot/github-action` runtime image pinned via the
upstream-recommended `RENOVATE_VERSION` env + magic comment +
`customManagers:githubActionsVersions` preset, so Renovate keeps the pin
updated.
- Custom regex manager tracks the `*_PACKAGE ?= <import-path>@<version>`
lines in `Makefile` (golangci-lint, swagger, actionlint, etc.) and
groups them into the same Go PR via `matchDatasources: ["go"]`.
- Post-upgrade tasks regenerate `assets/go-licenses.json` (`make tidy`)
and the SVG sprite (`make svg`), gated by an env-level command
allowlist.
- Replaces the standalone `cron-flake-updater` workflow — Renovate's nix
manager tracks `flake.nix` inputs and produces the same `flake.lock`
bump PRs on the regular weekly schedule.
- npm and gomod-replace pins live in `renovate.json5` only;
`updates@17.16.3` reads them from there too, so the standalone
`updates.config.ts` is gone and one source of truth covers both tools.

Fixes: https://github.com/go-gitea/gitea/issues/33386
Signed-off-by: silverwind <me@silverwind.io>
Signed-off-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: Giteabot <teabot@gitea.io>

.github/workflows/cron-renovate.yml

@@ -0,0 +1,31 @@
+name: cron-renovate
+
+on:
+  schedule:
+    - cron: "0 1 * * *" # daily at 01:00 UTC
+  workflow_dispatch:
+
+concurrency:
+  group: cron-renovate
+
+env:
+  RENOVATE_VERSION: 43.141.5 # renovate: datasource=docker depName=ghcr.io/renovatebot/renovate
+
+jobs:
+  cron-renovate:
+    runs-on: ubuntu-latest
+    if: github.repository == 'go-gitea/gitea' # prevent running on forks
+    timeout-minutes: 30
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: renovatebot/github-action@83ec54fee49ab67d9cd201084c1ff325b4b462e4 # v46.1.10
+        with:
+          renovate-version: ${{ env.RENOVATE_VERSION }}
+          configurationFile: renovate.json5
+          token: ${{ secrets.RENOVATE_TOKEN }}
+        env:
+          RENOVATE_BINARY_SOURCE: install # auto-install go/node toolchains needed by post-upgrade tasks.
+          RENOVATE_ALLOWED_POST_UPGRADE_COMMANDS: '["^make (tidy|svg)$"]'
+          RENOVATE_REPOSITORIES: '["go-gitea/gitea"]'