fix(ci): fetch full history so 'git describe --tags' works

The landing page showed 'version (no tag)' because actions/checkout@v4
defaults to a shallow clone (fetch-depth: 1) and pulls no tags. The
landing-page generator's 'git describe --tags --abbrev=0' then failed
and fell back to the placeholder.

Add fetch-depth: 0 to every checkout step in validate.yml + release.yml
so the runner sees all tags (current head: v0.5.0 + 6 commits).

.gitea/workflows/release.yml

@@ -12,6 +12,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Install dependencies
         run: |

.gitea/workflows/validate.yml

@@ -19,6 +19,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Install dependencies (Linux)
         if: matrix.os == 'ubuntu-latest'
@@ -58,6 +60,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Install dependencies
         run: |