fix(ci): normalize non-PEP440 versions before stamping pyproject.toml

If a tag or CI ref is not PEP 440 compliant (e.g. 'dev', 'nightly',
'snapshot-2024'), the previous detect_version stamped it raw into
pyproject.toml, which then broke 'pip install' with:
  configuration error: project.version must be pep440

Add a regex check after stripping the leading 'v'. If the result
is not PEP 440, substitute '0.0.0.dev0' and warn.

Pattern from ClaudeCodeFacts/gitea-python-ci-cd.md §3.

build-common.sh

@@ -23,6 +23,17 @@ detect_version() {
 
     VERSION_CLEAN="${VERSION#v}"
 
+    # Normalize non-PEP440 labels (e.g. "dev", "nightly", "snapshot") to a
+    # valid PEP440 dev release. Without this, pip/setuptools rejects
+    # pyproject.toml with: `project.version` must be pep440.
+    #
+    # Valid forms:   1.2.3, 1.2.3a1, 1.2.3rc2, 1.2.3.dev0, 1.2.3.post1, +local
+    # Invalid forms: dev, vdev, nightly, snapshot-2024
+    if ! [[ "$VERSION_CLEAN" =~ ^[0-9]+(\.[0-9]+)*((a|b|rc|\.dev|\.post)[0-9]+)*(\+[a-zA-Z0-9.]+)?$ ]]; then
+        echo "  Warning: '$VERSION_CLEAN' is not PEP440-compliant, using 0.0.0.dev0"
+        VERSION_CLEAN="0.0.0.dev0"
+    fi
+
     # Stamp version into pyproject.toml (single source of truth)
     sed -i "s/^version = .*/version = \"${VERSION_CLEAN}\"/" pyproject.toml
 }