fix(prometheus-rules): use increase() for the per-offer revenue rule

[bussyjd]

Summary

The recording rule x402:revenue:total_by_offer_current used a naive sum(counter) expression, which is wrong for any metric where the counter can reset across pod restarts. Prometheus counters are per-process by design — they reset to zero on every pod restart (rollout, OOM, eviction, node reschedule). A sum by (...) (counter) query therefore drops to zero whenever the verifier restarts, producing a misleading "0 requests" reading on offers with real on-chain traffic.

This PR fixes the rule to use increase(), which performs reset detection at query time across the samples held in the TSDB.

Before

- record: x402:revenue:total_by_offer_current
  expr: |
    sum by (offer_namespace, offer_name) (
      obol_x402_verifier_charged_requests_total
    )

After

- record: x402:revenue:7d_by_offer
  expr: |
    sum by (offer_namespace, offer_name) (
      increase(obol_x402_verifier_charged_requests_total[7d])
    )

Why increase([7d]) not [8d]

The TSDB is the canonical persistence layer (retention 8d). increase() needs samples on both sides of the window edge to do reset detection at the left edge of the window. A 7d window inside 8d retention gives a 1-day headroom so the rule keeps working at exactly the moment data ages out, instead of silently producing NaN/undercounts at the boundary.

Why the rename

The old names (total_by_offer_current, lifetime_by_offer) were aspirational against a finite retention window. The new name (7d_by_offer) matches what the expression actually returns and makes the bounded nature of the value explicit at the call site.

Canonical reference: Robust Perception "avoiding the counter-reset undercount".

Provenance

Found by the 14-PR integration test (plans/integration-test-results-final-20260524.md). The OBOL parity smoke surfaced it more visibly when a verifier restart produced a "0 req·24h" UI display on a row with real on-chain traffic.

Stacks on #527 (Helm-escape fix for the same file). Frontend consumer PR follows.

Test plan

• go build ./... clean
• go test ./internal/embed/... ./internal/x402/... green
• Verify the recording rule lands in Prometheus after obol stack up and returns a per-offer 7d count for a verifier that's been restarted at least once
• Frontend follow-up PR points at the renamed rule

[bussyjd]

Superseded by bundle PR #536 — closing in favor of the consolidated merge target. Original branch and history preserved.