Solve 27-university-department fixture against the released corpus gate

## Goal

Make `fixtures/websites/27-university-department` a `solved_candidate` using the released milestone stack, then prove `fixtures/solved/15-saas` remains solved in the target-plus-solved promotion lane.

## Baseline

- PHP Transformer: [`php-transformer-v0.2.7`](https://github.com/Automattic/blocks-engine/releases/tag/php-transformer-v0.2.7)
- Static Site Importer: [`v1.3.0`](https://github.com/Automattic/static-site-importer/releases/tag/v1.3.0)
- Promotion gate: [Automattic/static-site-importer#660](https://github.com/Automattic/static-site-importer/pull/660)
- Prior six-fixture evidence measured a 55.38% aligned visual mismatch. That evidence predates the merged navigation gap repair in #617, so establish a fresh target-only baseline before selecting repairs.

## Acceptance criteria

1. Run the SSI target lane for `27-university-department` on current accepted refs and capture editor, block-validity, and exact visual evidence.
2. Fix generic owning-layer causes only; no fixture-specific selectors or compensating output patches.
3. Reach `solved_candidate` with exact visual parity, valid native blocks, and no unaccepted runtime/HTML islands.
4. Run the promotion lane selecting `27-university-department` plus every fixture under `fixtures/solved/`.
5. Confirm both the target and `15-saas` retain `solved_candidate`; any `solved_regression` blocks promotion.
6. Promote fixture 27 into `fixtures/solved/` only from accepted gate evidence.

## Compatibility

Any generic transformer behavior change must document downstream compatibility impact and extension-path implications.

## AI assistance
- **AI assistance:** Yes
- **Tool(s):** OpenCode with OpenAI GPT-5.6 Sol
- **Used for:** Historical evidence review, release-baseline coordination, and issue drafting.

Start with the SSI target lane for fixtures/websites/27-university-department using php-transformer-v0.2.7, SSI v1.3.0, and the accepted promotion-gate reference, then capture editor, block-validity, and exact visual evidence. Compare the target with fixtures/solved/15-saas and inspect only generic owning-layer causes. Done means exact parity and valid native blocks for the target, followed by a promotion-lane run covering every fixture under fixtures/solved/ without regressions.

Written by the indexing model from the issue text.