Implement "Share to Taskwarrior" (receive sharing intent)

### Describe your improvement idea or feature request

Currently, the app cannot receive shared text or URLs from other applications via the system Share Sheet. This is a good feat for quickly capturing tasks (e.g., sharing a URL from a browser to creating a "Read this" task).

### How would you like to see it implemented?

- Integrate the receive_sharing_intent (or similar) package.

- Configure Android Manifest and iOS Info.plist to accept text/plain share intents.

- Handle the incoming intent by navigating to the "Add Task" screen and pre-filling the description field with the shared text/URL.

### Put here any screenshots or videos (optional)

_No response_

### How can we contact you (optional)

_No response_

### Would you like to work on this issue?

Yes

### By submitting this issue, I have confirmed that:

- [x] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

Start by inspecting the Android Manifest, iOS Info.plist, and the Add Task screen, then review receive_sharing_intent or a similar package. Done means text/plain shares from other apps are accepted on Android and iOS, open the Add Task screen, and prefill its description with the shared text or URL.

Written by the indexing model from the issue text.