ci: Tidy CI pipeline for readability and performance

Pipeline Modernisation:
- Update prefligit to prek (same project, renamed to avoid
  typosquatting)
- Replace custom rust-toolchain action with direct uvx rustup
  invocation
- Remove dependency on install scripts in favour of uvx tool
  execution
- Make sccache conditional on GH_APP_ID and GH_APP_PRIVATE_KEY
  availability

Workflow Restructuring:
- Rename workflows for improved clarity:
  * rust-checks.yml → ci-checks.yml (consolidates Rust + prek)
  * element.yml → deploy-element.yml
  * documentation.yml → deploy-docs.yml
  * release-image.yml → release-builds.yml (Docker + binaries)
  * mirror-images.yml → docker-mirror.yml
- Delete obsolete prefligit-checks.yml (merged into ci-checks.yml)
- Combine format and prek checks into single fast-checks job

Cache Strategy Improvements (release-builds.yml):
- Add restore-keys to Rust registry and cargo target caches
- Include Cargo.toml files in cargo-target cache key
- Consolidate separate apt-cache and apt-lib steps into single step
- Version APT cache with Dockerfile hash instead of static keys
- Add platform-specific Docker buildcache tags
- Simplify Rust registry paths (remove checkouts/src subdirs)

CI Execution Improvements:
- Add uv cache for faster uvx tool invocations (prek, rustup)
- Enable concurrency control with cancel-in-progress
- Fix BOM handling in pre-commit

Dependency Management:
- Add renovate.yml workflow for scheduled dependency checking
- Configure renovate.json to monitor .forgejo/ and .github/ dirs
- Group non-major GitHub Actions updates into single PRs
- Set PR limits: 3 concurrent, 2 per hour

.forgejo/workflows/deploy-docs.yml

@@ -0,0 +1,74 @@
+name: Deploy / Documentation
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+concurrency:
+  group: "pages-${{ github.ref }}"
+  cancel-in-progress: true
+
+jobs:
+  docs:
+    name: Build and Deploy Documentation
+    runs-on: ubuntu-latest
+    if: secrets.CLOUDFLARE_API_TOKEN != ''
+
+    steps:
+      - name: Sync repository
+        uses: https://github.com/actions/checkout@v4
+        with:
+          persist-credentials: false
+          fetch-depth: 0
+
+      - name: Setup mdBook
+        uses: https://github.com/peaceiris/actions-mdbook@v2
+        with:
+          mdbook-version: "latest"
+
+      - name: Build mdbook
+        run: mdbook build
+
+      - name: Prepare static files for deployment
+        run: |
+          mkdir -p ./public/.well-known/matrix
+          mkdir -p ./public/.well-known/continuwuity
+          mkdir -p ./public/schema
+          # Copy the Matrix .well-known files
+          cp ./docs/static/server ./public/.well-known/matrix/server
+          cp ./docs/static/client ./public/.well-known/matrix/client
+          cp ./docs/static/client ./public/.well-known/matrix/support
+          cp ./docs/static/announcements.json ./public/.well-known/continuwuity/announcements
+          cp ./docs/static/announcements.schema.json ./public/schema/announcements.schema.json
+          # Copy the custom headers file
+          cp ./docs/static/_headers ./public/_headers
+          echo "Copied .well-known files and _headers to ./public"
+
+      - name: Setup Node.js
+        uses: https://github.com/actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Install dependencies
+        run: npm install --save-dev wrangler@latest
+
+      - name: Deploy to Cloudflare Pages (Production)
+        if: github.ref == 'refs/heads/main' && vars.CLOUDFLARE_PROJECT_NAME != ''
+        uses: https://github.com/cloudflare/wrangler-action@v3
+        with:
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          command: pages deploy ./public --branch="main" --commit-dirty=true --project-name="${{ vars.CLOUDFLARE_PROJECT_NAME }}"
+
+      - name: Deploy to Cloudflare Pages (Preview)
+        if: github.ref != 'refs/heads/main' && vars.CLOUDFLARE_PROJECT_NAME != ''
+        uses: https://github.com/cloudflare/wrangler-action@v3
+        with:
+          accountId: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
+          apiToken: ${{ secrets.CLOUDFLARE_API_TOKEN }}
+          command: pages deploy ./public --branch="${{ github.head_ref || github.ref_name }}" --commit-dirty=true --project-name="${{ vars.CLOUDFLARE_PROJECT_NAME }}"