Filter Link Health reports and add reviewed URL edits

[wpgaurav]

Makes the Link Health report filterable by result status, source type, and URL/source-title text. Filters are applied before 50-row pagination and stay active during live updates, navigation, and CSV export.

Each row now offers Replace URL and Unlink for its source post. Preview shows the matching-anchor count; Apply requires the current actor's expiring token and an unchanged source fingerprint. A binary compare-and-swap protects against saves arriving after validation. Edits preserve surrounding markup, fragments, child text/media, native button structure, revisions, and post-save cache notifications. URLs duplicated in serialized block settings defer to the post editor instead of risking an inconsistent block. Percent-encoded URLs are preserved.

The edit dialog pauses report replacement without stopping scan progress. Changed inputs, cancelled previews, and late responses cannot authorize a different edit. Successful saves reconcile the report, retaining unchanged results and marking new destinations unchecked.

Validation:

• PHP syntax, WordPress coding standards/PHP 7.4 compatibility, 167 PHP tests / 892 assertions, and 18 JavaScript tests passed. Utility cases also passed against newer local core; the native-markup and serialized-settings guard ran on Gatilab's actual core.
• On Gatilab: 200 broken links filtered correctly; page two contained 50 broken rows; CSV exported exactly the filtered 200. Combined status/type filters and source-title search passed.
• A temporary fixture exercised replacement of three anchors, preserved fragments, unlinking text/image/button anchors, revision creation, source readback, public frontend output, and percent encoding.
• At 390px, the dialog measured 342px with no overflow. Switching an invalid replacement input to Unlink still produced a valid preview.
• Fixtures and revisions were removed after checking their expected content. All 19 module settings, 1,203 existing post/page content/type/status hashes, and existing link-report metadata matched the snapshot. All 150 deployed runtime files matched the package.

Visual-check limitation: Gutenberg's iframe canvas stayed empty in the test browser for both the edited fixture and an untouched control. No successful canvas-validation claim is made; stored block structure, surrounding markup, revisions, and public frontend output were verified. The existing iframe visual release gate remains tracked separately.

See docs/link-health-edit-verification.md for details and recovery location. readme.txt and README.md describe the new filters and edit scope.