💡 Add Support for New Committee Governance Actions

### Area

Proposal Pillar

### Is there new design needed?

No

### What?

Enable creation and on-chain submission of **Update Committee** governance actions in GovTool. This includes changes to **members**, **threshold (numerator/denominator)**, or **terms** as defined in CIP-1694.

### Required Fields:
- Title
- Abstract
- Motivation
- Rationale
- Numerator
- Denominator
- New Committee Member(s) (bech32)
- Expiry Epoch
- Remove Committee Member(s) (bech32)
- Reference Links

### Why?

- The **Update Committee** action is critical for adjusting **constitutional governance structures**, but it’s not yet supported for proposal submission in GovTool.
- Enables changes to **committee composition**, **voting thresholds**, and **expiry conditions** of members.
- Keeps the governance framework **adaptive and up-to-date** with the needs of the community.

### How?

- Form UI should support dynamic entry of bech32 member addresses (both add/remove).
- Threshold inputs must be integer values and validated.
- Include expiry epoch field (positive integer).
- Link metadata generation and on-chain submission to this new action type.

### (Optional) User Story with acceptance criteria

- [ ] All required fields are implemented, validated, and saved.
- [ ] Metadata matches CIP-1694 schema and is hashable.
- [ ] Submission proceeds correctly on-chain and appears in voting & outcomes.