feat(ui): strengthen generated-index readability and focus states

[seonghobae]

Buyer-visible problem

The generated directory index is the product. Its rows, empty state, hover state, focus state, and dark-mode presentation must remain readable without relying on low opacity, emoji-specific rendering, or an underline that runs beneath a decorative icon.

Current-base implementation

This branch was rebuilt from protected master commit 060abbb0ea40a9b1b3bcd5e322272324b6256a30, after CSP PR #363 integrated. It preserves the exact emitted-style/CSP byte-identity contract and applies one bounded presentation change:

• separate adjacent rows with li + li, avoiding a final-row exception;
• replace opacity-based empty-state text with explicit light and dark foreground colors;
• retain role="status", the existing deterministic information icon, aria-hidden="true", and reduced-motion behavior;
• underline only the textual span on hover and :focus-visible, while retaining the existing 2px outline around the complete interactive target;
• place dark-mode overrides after their corresponding base rules; and
• leave file order, URLs, escaping, CSP, indexing policy, hidden-file policy, and filesystem behavior unchanged.

Test-first verification

GeneratedIndexReadabilityTest exercises real generated index.html output for:

1. parent, first, middle, and last row order;
2. exactly one semantic empty-state row;
3. adjacent-row separator structure;
4. explicit light/dark empty-state colors and absence of opacity;
5. dark-mode cascade order;
6. text-only hover/focus underline with the full-target outline preserved;
7. reduced-motion retention; and
8. numeric sRGB contrast thresholds for ordinary text and authored focus colors.

CspHashTest continues to independently recompute the hash from the exact emitted <style> bytes. CHANGELOG.md and docs/doctoring/generated-index-readability.md record the scope, WCAG 2.2 engineering basis, APA 7 references, calculated ratios, and the explicit boundary that automated source tests are evidence rather than a formal conformance claim.

Exact-head gates

At head fd3749a58714aeb27ac6774ba86a8b72cf6354f5, CI including JaCoCo coverage verification, Security Scan, Semgrep, and CodeRabbit status have succeeded, and no unresolved review thread is present. The PR is ready for review but must not merge until an independent non-author approval applies to this exact head and every repository-required gate remains successful. Queued, pending, skipped-required, cancelled, absent, stale-head, or failed checks are not success.

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📥 Commits

Reviewing files that changed from the base of the PR and between 060abbb and fd3749a.

📒 Files selected for processing (4)

• CHANGELOG.md
• docs/doctoring/generated-index-readability.md
• src/main/kotlin/html4tree/main.kt
• src/test/kotlin/html4tree/GeneratedIndexReadabilityTest.kt

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