Add taxonomy annotations and validate @cap/@feat cardinality in product scenarios

Summary

Introduce taxonomy annotations for all checked-in product .feature scenarios. Then enforce annotation cardinality in the integration framework standards checker.

Rationale

The current suite has no consistent use of @cap and @feat tags. Enforcing the rule now would fail all existing product scenarios. The annotation rollout must complete before standards-check rejects missing or duplicate tags.

Affected areas

• tests/framework/suites/it/features/**/*.feature
• tests/framework/suites/ui/features/**/*.feature
• tests/framework/cmd/standards/main.go, specifically checkFeatures

Required changes

1. Define and apply exactly one @cap tag and one @feat tag to every product scenario.
2. Update checkFeatures to parse scenario boundaries.
3. Make checkFeatures reject product scenarios with zero or multiple @cap tags.
4. Make checkFeatures reject product scenarios with zero or multiple @feat tags.
5. Preserve the existing feature validation checks.

Acceptance criteria

• Every checked-in product scenario has exactly one @cap tag and exactly one @feat tag.
• standards-check reports missing and duplicate taxonomy annotations per scenario.
• Existing feature validation remains active.
• Tests cover valid, missing, and duplicate annotations.

Backlinks

• Pull request: https://github.com/wso2/api-platform/pull/3404
• Review comment: https://github.com/wso2/api-platform/pull/3404#discussion_r3956888954
• Requested by: @nimsara66