docs: budget metric and alert still describe every cap hit as deferred

[SebTardif]

The budget counter and its alert still describe every hit as "deferred until the next cycle." That is only true for one of the two events.

attune_budget_exhausted_total increments in recordBudgetBlock (internal/controller/resize.go) for both:

• BudgetExhausted: this increase fits the configured cap, but not the budget left in this cycle. A later cycle can run it.
• IncreaseExceedsBudget: one container's increase is larger than maxCpuIncreasePerMinute, maxMemoryIncreasePerMinute, maxTotalCpuIncrease, or maxTotalMemoryIncrease. Waiting does not help. Raise that cap or lower the target.

Stale text today:

• docs/reference/metrics.md, section attune_budget_exhausted_total, mentions only the per-cycle cap and says the resize was deferred.
• charts/attune/templates/prometheusrule.yaml, alert AttuneBudgetExhausted, says the per-cycle budget was exhausted, that resizes are being deferred, and names only maxTotalCPUIncrease / maxTotalMemoryIncrease.
• docs/guides/prometheus-setup.md table row says "Resize budget exhausted for 30m".

This issue is reserved for a first-time contributor. Please leave the ready label off.

Done when

• docs/reference/metrics.md says the counter covers both events, including the per-minute caps.
• The AttuneBudgetExhausted annotation tells the reader to check the policy event (BudgetExhausted vs IncreaseExceedsBudget) and names the per-minute fields as well as the per-cycle fields.
• The prometheus-setup table row matches that distinction.
• charts/attune/tests/prometheusrule_test.yaml has a case, with the rule enabled, that asserts the AttuneBudgetExhausted annotation mentions IncreaseExceedsBudget and maxCpuIncreasePerMinute. Follow the existing default-alert cases in that file (matchRegex on the rendered rule). With every rule enabled, this alert is spec.groups[0].rules[5].
• make helm-unittest passes.

Pull request

Use a title like docs: describe both budget cap events on the alert. The subject after docs: must start with a lowercase letter. Commit with git commit -s.