fix(php-transformer): aggregate rejected artifact diagnostics

[chubes4]

Summary

• Replaces terminal per-file rejected-input diagnostics with one bounded artifact_inputs_rejected aggregate containing exact counts and allowlisted samples.
• Keeps detailed normalization diagnostics available to plans while making final direct and staged results consistent.
• Related to Surface and bound oversized artifact report files instead of silently ignoring them #1242 and SSI consumer projection PR fix(report): bound compiler diagnostic projections static-site-importer#1577.
• DLA producer semantics remain unchanged; cc915578 is consumer context only.

Verification

• php tests/unit/artifact-normalizer-source-budget.php
• php tests/contract/run.php
• composer parity (305 fixtures)

AI Assistance

Implemented directly with OpenAI gpt-5.6-terra via OpenCode. GPT-6 Astra was used through OpenCode for orchestration and review.