💡 Add Archiving Feature for Proposals

### Area

Proposal Pillar

### Is there new design needed?

Yes

### What?

Currently, proposals remain in the app indefinitely unless they are submitted as a governance action on-chain, which requires a **100k ADA deposit**. This means users cannot remove proposals they no longer need, leading to clutter and prolonged discussions on outdated proposals.

A new **"Archive"** feature should be introduced to allow users to move proposals they no longer need into an archived state. Archived proposals should:
- Be hidden by default from the active proposal list.
- Be **read-only** (cannot be edited).
- Have an **"Unarchive"** option when viewing details.

### Why?

- Prevents unnecessary discussions on outdated proposals.
- Helps users manage proposals more effectively.
- Reduces clutter by allowing users to focus only on relevant proposals.
- Provides an alternative to submitting a governance action for proposal closure.

### How?

- Add an **"Archive"** option for proposals, moving them to an archived state.
- Update filters to include a new **"Archived"** category (not visible by default).
- Ensure archived proposals are **read-only** to prevent further modifications.
- Add an **"Unarchive"** button on the proposal details page to restore archived proposals.
- Ensure archiving/unarchiving updates the UI dynamically without requiring a refresh.

### (Optional) User Story with acceptance criteria

- [ ] Users can **archive** proposals they no longer need.
- [ ] A new **"Archived"** filter option is added (archived proposals are hidden by default).
- [ ] Archived proposals are **read-only**.
- [ ] Users can **unarchive** a proposal from its details page.
- [ ] UI updates dynamically upon archiving/unarchiving.