feat: add local PyPI repository support (#50)

## Summary
- Upload Python wheels/sdists to local PyPI repos with filename validation
- PEP 503 simple index computed on-demand from stored files
- Package names normalized per PEP 503 (lowercase, hyphens)
- Overwrites rejected (409 Conflict)

## Test plan
- [x] Build wheel with `uv build` → upload → verify simple index HTML → `uv pip install` from local repo
- [x] Bad filename rejection (400)
- [x] Overwrite rejection (409)
- [x] Hash integrity verification on download

Reviewed-on: #50
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

internal/api/v1/proxy.go

@@ -115,10 +115,15 @@ func (h *ProxyHandler) handleLocal(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if remote.PackageType == models.PackageTerraform {
+	switch remote.PackageType {
+	case models.PackageTerraform:
 		if h.serveTerraformMirror(w, r, remote, path) {
 			return
 		}
+	case models.PackagePyPI:
+		if h.servePyPIMirror(w, r, remote, path) {
+			return
+		}
 	}
 
 	h.serveLocalFile(w, r, localName, path)
@@ -149,6 +154,24 @@ func (h *ProxyHandler) serveTerraformMirror(w http.ResponseWriter, r *http.Reque
 	return false
 }
 
+func (h *ProxyHandler) servePyPIMirror(w http.ResponseWriter, r *http.Request, remote *models.Remote, path string) bool {
+	if path == "simple" || path == "simple/" {
+		h.local.ServePyPIIndex(w, r, remote.Name)
+		return true
+	}
+
+	if strings.HasPrefix(path, "simple/") {
+		pkg := strings.TrimPrefix(path, "simple/")
+		pkg = strings.TrimSuffix(pkg, "/")
+		if pkg != "" && !strings.Contains(pkg, "/") {
+			h.local.ServePyPIPackageIndex(w, r, remote.Name, pkg)
+			return true
+		}
+	}
+
+	return false
+}
+
 func (h *ProxyHandler) serveLocalFile(w http.ResponseWriter, r *http.Request, repoName, path string) {
 	file, err := h.db.GetLocalFile(r.Context(), repoName, path)
 	if err != nil {