feature: public anonymity-set analytics dashboard

[tech-adrian]

Problem

There's no public way to see how deep the anonymity set actually is (total commitments, deposit/withdraw volume over time) short of manually paging through get_commitments_page or reading raw chain events. Users deciding whether it's currently "safe" to withdraw (i.e. whether the pool has enough recent activity to blend into) have no signal to go on.

Why it matters

Anonymity-set size is the actual privacy guarantee a shielded pool provides — a pool with 3 deposits offers far less protection than one with 3,000, and today a user has no way to know which situation they're in without manually querying the contract.

Scope

• New frontend/src/lib/analytics.ts: aggregate public, non-deanonymizing stats from pool events — total commitments (get_next_index), deposit/withdrawal counts over time, currently-known root history — with no linkage to which specific commitment belongs to which withdrawal (that link is exactly what the pool is designed not to reveal).
• New frontend/src/app/stats/page.tsx: a public dashboard rendering pool depth over time, recent deposit/withdraw counts, and a simple "anonymity set size" figure.
• frontend/src/lib/indexer.ts: expose the aggregate counts the dashboard needs without exposing per-note linkage.
• Tests confirming the aggregation logic never surfaces amount/recipient linkage between a specific deposit and a specific withdrawal.
• README.md: link the new stats page.

Acceptance criteria

• A public page shows pool depth and activity trends over time.
• The dashboard's data model is verified (by test) to never expose a deposit-to-withdrawal linkage, only aggregate counts.

[dimin4241-svg]

Hi! I’ve worked with privacy-preserving analytics, event aggregation, and Next.js dashboards. I’ll keep the data model aggregate-only, expose pool depth and activity trends, and add tests proving no deposit-to-withdrawal linkage is returned. I can open a focused draft within 48 hours after assignment. Please assign this issue to me.

[PASdeco]

Hi team, I'd love to take on #145.

I’ve worked with Next.js/React + TypeScript and dashboard/charting. I’ve already looked at frontend/src/lib/indexer.ts and the pool's get_next_index / get_commitments_page flow.

My plan: create frontend/src/lib/analytics.ts to aggregate public stats, total commitments, deposit/withdraw counts over time, root history, with no deposit-to-withdrawal linkage, expose aggregates via indexer.ts, and build frontend/src/app/stats/page.tsx for pool depth, activity trends and anonymity set size. I’ll add tests to verify no linkage is exposed and update README.md. Will ensure npm test passes.

Can start immediately if assigned, thanks!