Update OpenAPI tags/grouping to match new IA: Overview/Assets/Wallets/Soroban/Rankings

[christabel888]

Context: OpenAPI tags currently follow the existing route grouping (e.g. tag = "Analytics" seen in analytics_dashboard.rs). As new endpoints land under network/soroban/wallets/rankings, the tags should match the frontend's new nav IA (Overview/Assets/Wallets/Soroban/Rankings) rather than accumulating ad-hoc tags.

Where:

• src/openapi.rs -- the #[derive(OpenApi)] tag list
• Each new handler's #[utoipa::path(..., tag = "...")]

What to do:

• Define the tag set once the new endpoints from this batch exist, and retrofit consistent tags across Add /api/v1/stats/summary endpoint: DAA, tx count 24h, payment volume 24h, active soroban contracts #1, Add /api/v1/assets/{code}/insights endpoint #11-Add governance insights endpoint: proposal momentum, voter turnout #14, Add /api/v1/network/daily-active-accounts time-series endpoint #15-Add /api/v1/network/fee-trends endpoint #19, Add /api/v1/soroban/active-contracts endpoint #21-Add /api/v1/soroban/top-contracts and /new-deployments endpoints #24, Add /api/v1/wallets/{address}/portfolio endpoint #25-Add /api/v1/wallets/{address}/largest-transfers endpoint #29, Add /api/v1/rankings/top-movers endpoint: 24h percent change by holders/volume #33, Add /api/v1/rankings/assets endpoint: top assets by holders and volume #39.

Suggested approach:

1. Wait until most of Add /api/v1/stats/summary endpoint: DAA, tx count 24h, payment volume 24h, active soroban contracts #1, Add /api/v1/assets/{code}/insights endpoint #11-Add governance insights endpoint: proposal momentum, voter turnout #14, Add /api/v1/network/daily-active-accounts time-series endpoint #15-Add /api/v1/network/fee-trends endpoint #19, Add /api/v1/soroban/active-contracts endpoint #21-Add /api/v1/soroban/top-contracts and /new-deployments endpoints #24, Add /api/v1/wallets/{address}/portfolio endpoint #25-Add /api/v1/wallets/{address}/largest-transfers endpoint #29, Add /api/v1/rankings/top-movers endpoint: 24h percent change by holders/volume #33, Add /api/v1/rankings/assets endpoint: top assets by holders and volume #39 exist before doing this audit -- it's a consistency pass, not something to do preemptively.
2. Go endpoint by endpoint, assign a tag matching the frontend nav IA (Overview/Assets/Wallets/Soroban/Rankings), and update each #[utoipa::path(..., tag = "...")].
3. Regenerate /api-docs and manually check the grouping renders sensibly, not just that the code compiles.

Watch out for:

• This touches a lot of files across a lot of PRs that may have landed at different times with inconsistent tags already -- budget time for cleanup, not just addition.

Definition of done:

• /api-docs groups endpoints under Overview/Assets/Wallets/Soroban/Rankings tags matching the frontend nav