Add low member count warning for rotational pools

[khanavi272-spec]

Description

This PR adds a non-blocking warning banner to the Rotational Pool detail page when the pool member count falls to 2 or fewer.

The banner informs users that the pool has very few members remaining and suggests inviting more members or planning for a shorter cycle.

Closes #150

Type of Change

• feat: new feature
• fix: bug fix
• chore: maintenance, tooling, dependencies
• docs: documentation only
• refactor: code restructuring (no functional changes)
• test: adding or updating tests

How Has This Been Tested?

• cargo test passes (smart contracts)
• pnpm build succeeds (frontend)
• pnpm lint passes (frontend)
• Manual testing

Manual Testing

• Verified the warning banner is displayed for rotational pools with 2 or fewer members.
• Verified the banner is informational only and does not block any pool actions.
• Verified pools with more than 2 members are unaffected.

Checklist

• My code follows the project's coding style.
• I have reviewed my own code.
• I have kept the change focused on the requested feature.

Closes #147

[Sendi0011]

@khanavi272-spec Nice, clean addition — really like that this is scoped specifically to Rotational pools, since that's where a missing deposit really does hit harder with fewer members. Reusing the existing members_count field and matching the existing warning-banner style (like the paused-pool one) instead of inventing something new is exactly right. One tiny non-blocking thing: a couple of the new lines have slightly different indentation than the rest of the file — might be worth a quick formatter pass, but not something I'd hold this up for. Approving!