Remove 30-day sandbox lifetime limit from persistence docs (#94)

The sandbox persistence documentation no longer references
the 30-day maximum lifetime restriction.

Author: beran-t

docs/sandbox/persistence.mdx

@@ -276,13 +276,6 @@ If you resume the sandbox, the service will be accessible again but you need to
 
 ## Limitations while in beta
 
-### Lifecycle duration
-- A sandbox can exist for **up to 30 days** from the initial `create` call.
-- After 30 days, sandbox data **may be deleted** and the sandbox can no longer be resumed.
-- Attempting to resume a deleted or non-existent sandbox will result in:
-  - `NotFoundError` in the JavaScript SDK
-  - `NotFoundException` in the Python SDK
-
 ### Pause and resume performance
 - Pausing a sandbox takes approximately **4 seconds per 1 GiB of RAM**
 - Resuming a sandbox takes approximately **1 second**
@@ -292,4 +285,3 @@ If you resume the sandbox, the service will be accessible again but you need to
   - **24 hours** on the **Pro tier**
   - **1 hour** on the **Base tier**
 - After a sandbox is paused and resumed, the continuous runtime limit is **reset**
-- The **30-day total lifetime limit** still applies regardless of how many times the sandbox is paused or resumed