Bump GitHub Actions to Node-24-native majors (drop Node 20 deprecation)

Node 20 actions are deprecated (forced to Node 24 from 2026-06-16). Pin to the
current majors that run on Node 24:
- book.yml: checkout v4→v6, configure-pages v5→v6, upload-pages-artifact v3→v5, deploy-pages v4→v5
- .gitea/conformance.yml: checkout v4→v6, setup-python v5→v6, upload-artifact v4→v7

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: supachai-j

.gitea/workflows/conformance.yml

@@ -11,8 +11,8 @@ jobs:
   validate:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@v6
+      - uses: actions/setup-python@v6
         with:
           python-version: "3.13"
       - name: Validate OKF conformance (blocks merge on failure)
@@ -22,7 +22,7 @@ jobs:
       - name: Regenerate viewer
         run: python3 tools/okf-viz.py --name "Self-OKF Wiki"
       - name: Upload viewer artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: okf-viz
           path: wiki/viz.html

.github/workflows/book.yml

@@ -22,7 +22,7 @@ jobs:
     env:
       MDBOOK_VERSION: "0.4.40"
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Install mdBook
         run: |
           curl -sSL "https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz" \
@@ -71,8 +71,8 @@ jobs:
           }
           gen "$PWD/book/book/print.html"    "$PWD/book/book/okf-manual-th.pdf"     "คู่มือ Open Knowledge Format (OKF)" "เรียบเรียง Supachai Jaturaprom [TumEz] · เขียนโดย Claude Code — Opus 4.8 (AI)" "$PWD/book/src/SUMMARY.md" "$PWD/book/src" || true
           gen "$PWD/book-en/book/print.html" "$PWD/book/book/en/okf-manual-en.pdf" "The Open Knowledge Format (OKF) Handbook" "Compiled by Supachai Jaturaprom [TumEz] · Written by Claude Code — Opus 4.8 (AI)" "$PWD/book-en/src/SUMMARY.md" "$PWD/book-en/src" || true
-      - uses: actions/configure-pages@v5
-      - uses: actions/upload-pages-artifact@v3
+      - uses: actions/configure-pages@v6
+      - uses: actions/upload-pages-artifact@v5
         with:
           path: book/book
 
@@ -84,4 +84,4 @@ jobs:
       url: ${{ steps.deployment.outputs.page_url }}
     steps:
       - id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@v5