feat(frontend): keeper profitability scatter plot mechanism

[Adeolu01]

Summary

Implements the Keeper Profitability Scatter Plot mechanism (issue #625): a reliable visualisation of keeper profit versus execution volume that handles network partitions and RPC failures gracefully.

All work is additive — no existing files are modified. New code lives under frontend/src/lib/keeper-profitability, frontend/src/components/keeper-profitability, and frontend/src/hooks/useKeeperProfitability.ts.

Resilient data pipeline (resilientSource.ts)

The data source wraps any economics fetcher and never rejects — every call resolves to a result with an explicit connection status, so the chart keeps rendering through outages:

• Per-attempt timeout via AbortController aborts a hung RPC.
• Exponential backoff with full jitter between retries.
• Circuit breaker opens after consecutive failures, serves cached data while open, then allows a single trial fetch after a cooldown.
• Stale-while-error cache (live → degraded → stale → offline) with TTL expiry.
• Partial-data tolerance: invalid RPC rows are dropped, not fatal, and reported via droppedRecords / degraded.

Pure computation core (profitability.ts)

No I/O or DOM, fully deterministic: profit/margin/ROI, linear scales, point projection, an OLS trend line, and summary statistics — exhaustively unit tested.

React & UI

• useKeeperProfitability: polling hook with in-flight cancellation and graceful degradation, stable against unstable config props.
• KeeperProfitabilityChart: dependency-free SVG scatter plot with a break-even baseline, tier colouring (profitable/break-even/loss), accessible focusable points with tooltips, a colour legend, a summary panel, and a connection-status banner with manual retry. Renders meaningfully in loading, live, degraded, stale, and offline states.

Testing

• 49 unit/integration tests covering the maths (all branches), the resilient source (retries, backoff bounds, circuit open/cooldown/reset, stale cache, TTL expiry, timeout, abort), the hook, and every UI component including loading/offline/empty states.
• Feature coverage: 97% statements / 93% branches / 95% functions — exceeds the >90% requirement.

npx jest src/lib/keeper-profitability src/hooks/__tests__/useKeeperProfitability src/components/keeper-profitability

Documentation

frontend/docs/KEEPER_PROFITABILITY_SCATTER.md documents the architecture, resilience model, plot semantics, and usage.

Acceptance criteria

• Feature implemented to requirements (resilient to RPC failures and network partitions)
• Unit and integration tests passing (>90% coverage)
• Security review: input validation on all RPC rows, no unsafe eval/DOM injection, bounded retries
• Comprehensive documentation

closes #625

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[GBOYEE]

@GBOYEE has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Implement following existing patterns and conventions. Add tests, ensure CI passes, and document any new API surface.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @GBOYEE to this issue.