chore: ban nested ternaries via biome

[SgtPooki]

Summary

• Enable Biome style/noNestedTernary: error repo-wide so nested ternaries fail CI.
• Fix the two existing violations:
  • apps/web/src/pages/Landing.tsx: replace nested ternary picking approvedSpDashboardUrl by network with a Record<Network, ...> lookup (gains compile-time exhaustiveness if Network grows).
  • apps/backend/src/deal-addons/strategies/ipni.strategy.ts: replace inline nested ternary on failureReason with a new getErrorMessage helper.
• Add getErrorMessage(error: unknown): string in apps/backend/src/common/logging.ts. Derives from toStructuredError (so redaction is inherited) and prefers cause.message over outer message when the cause is a real Error — preserves PR feat(ipni): expose failureReason as top-level field on ipni_tracking_failed #491 / issue IPNI xxx root CID not verified #473 intent of keeping failureReason aggregable in BetterStack/Grafana (no high-cardinality deal IDs in the flat field). Guards against non-Error causes leaking "Non-Error thrown".

Peer-reviewed in three rounds via Claude, Cursor, and Gemini agents; consensus approved after the cause-preferred semantics were restored and the cause.type === "error" guard added.

Test plan

• pnpm lint:check — passes (the only remaining warning is in an untracked scratch file).
• pnpm build (apps/backend) — passes.
• pnpm typecheck (apps/web) — passes.
• pnpm vitest run src/common/logging.spec.ts src/deal-addons/strategies/ipni.strategy.spec.ts — 23/23 pass.
• Post-merge: confirm BetterStack WHERE event = 'ipni_tracking_failed' GROUP BY failureReason still buckets cleanly (no deal-ID prefix regression).

[SgtPooki]

self review.. lgtm

[Copilot]

Pull request overview

This PR enforces a consistent code style across the repo by enabling Biome’s style/noNestedTernary rule as an error (CI-failing), and updates the two existing nested-ternary violations to compliant, clearer implementations. It also centralizes “flat” error-message extraction logic to preserve low-cardinality failureReason fields for logging/observability use cases.

Changes:

• Enable Biome style/noNestedTernary: "error" repo-wide.
• Refactor the web Landing page’s approved-SP dashboard URL selection to a Record<Network, ...> lookup.
• Add getErrorMessage(error: unknown) in backend logging utilities and use it for ipni_tracking_failed.failureReason.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
biome.json	Enforces noNestedTernary as an error to prevent nested ternaries repo-wide.
apps/web/src/pages/Landing.tsx	Replaces nested ternary network URL selection with a typed lookup map.
apps/backend/src/deal-addons/strategies/ipni.strategy.ts	Uses getErrorMessage for failureReason to avoid nested ternary and keep logs aggregable.
apps/backend/src/common/logging.ts	Introduces getErrorMessage built on toStructuredError redaction semantics.