refactor: move auth token to HttpOnly cookie, fix CORS and artefacts

Backend:
- Set JWT as HttpOnly cookie on login, add cookie fallback in auth middleware
- Add /auth/logout endpoint to clear cookie
- Fix CORS to echo origin with Allow-Credentials for withCredentials requests
- Make SPA static serving optional via SERVE_SPA config flag

Frontend:
- Remove manual token management; rely on HttpOnly cookie + withCredentials
- Simplify auth-slice to authenticated boolean flag
- Fix Artefact interface to match backend fields (sha256Hash, fileName, fileSize)
- Fix artefact upload endpoint and send version in FormData
- Use KiB/MiB for file size display
- Move Redux hooks from store/hooks to hooks/store

internal/auth/handler.go

@@ -28,5 +28,16 @@ func (h *Handler) Login(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, resp)
+	// Set JWT as HttpOnly cookie so the frontend doesn't need to manage it.
+	// The browser sends it automatically on every request.
+	maxAge := h.svc.ExpiryHrs() * 3600
+	c.SetCookie("pipely_token", resp.Token, maxAge, "/", "", false, true)
+
+	c.JSON(http.StatusOK, gin.H{"message": "Login successful"})
+}
+
+func (h *Handler) Logout(c *gin.Context) {
+	// Clear the auth cookie by setting MaxAge=-1
+	c.SetCookie("pipely_token", "", -1, "/", "", false, true)
+	c.JSON(http.StatusOK, gin.H{"message": "Logged out"})
 }