Materialize pages before optional URL hydration

[chubes4]

Fixes #815

Summary

• Persist and materialize a deterministic page_ready batch checkpoint after all requested HTML and stylesheet/font-critical dependencies are collected.
• Continue optional asset hydration through the existing strict complete-snapshot collection path, then materialize the deterministic final artifact.
• Report page-ready routes as materialized progress during cooperative deadline continuations.

Evidence

• npm test passed: 44 selected checks, 0 failed.
• php tests/smoke-url-batch-import.php passed, including interruption after page readiness, resume, and byte-for-byte final artifact equivalence with a clean run.
• URL collector and URL import runtime smokes passed; all production PHP files passed php -l; git diff --check passed.
• Scoped Homeboy whitespace gate passed: homeboy review lint --file includes/class-static-site-importer-url-batch-import.php --sniffs Generic.WhiteSpace.ScopeIndent,Generic.WhiteSpace.ArbitraryParenthesesSpacing,Squiz.ControlStructures.ControlSignature,WordPress.Arrays.ArrayKeySpacingRestrictions --placement local --summary.

Compatibility and Schema

• The existing static-site-importer/url-site-batch-run/v1 manifest schema remains unchanged. page_ready is an additive batch state and reuses the existing batch result receipt field.
• Strict callers retain complete-snapshot collection semantics. Page-first materialization is limited to deadline-governed cooperative URL batches.
• A resumed page-ready batch verifies its persisted snapshot digest before optional hydration; mismatch fails closed.

AI assistance

OpenAI gpt-5.6-sol via OpenCode implemented the checkpoint, optional hydration continuation, formatting, and deterministic tests. Chris Huber reviewed and remains responsible for every line.