Add utility modules, live link audits, and backend improvements for 1.7.0

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Adds three optional modules for 1.7.0: Content Tools duplicates native posts/pages into drafts, Link Health checks stored public-content links, and Site Activity keeps a bounded private history. All three start disabled; weekly link scans are separately opt-in.

Link Health now gives administrators live feedback and continuous bounded checking while its workspace is open. The page shows waiting/checking/stopping/completed states, a progress bar, completed posts, checked links, and refreshed results. Stop finishes the current worker safely; Resume preserves the cursor. Each results page contains up to 50 links across sources, with one pager and a full-width table. This resolves slow-looking external-cron scans, static status text, sparse per-source result pages, and rejected stop requests during active batches.

The live endpoint requires administrator access and a valid nonce. Run identifiers prevent stale browser requests from acting on another scan; worker leases and client request ordering prevent overlaps and late responses overriding Stop. Public-source validation, SSRF guards, confirmed GET 404/410 classification, inconclusive transport errors, cached checks, native forms, and CSV export remain in place. A small result-count index supports pagination and follows opt-in uninstall cleanup.

The backend also has consistent desktop/phone controls, local Tabler icons, a color-adaptive admin mark, complete breadcrumbs and back buttons, and responsive module-guidance sidebars. Listing assets include the restrained Apple-inspired icon/bento banner and real backend screenshots. readme.txt now describes 1.7.0, live scan behavior, 50-result pagination, actual storage, and feature limits.

Validation:

• PHP syntax, WordPress coding standards/PHP 7.4 compatibility, 158 PHP tests / 844 assertions, and 13 JavaScript tests. Cancellation and stale-browser regressions were observed failing before the fix.
• Translation freshness, source/ZIP manifests, distribution guards, and listing asset checks.
• Gatilab (WordPress 7.1.2/PHP 8.5.10): live checks advanced 88 → 176 without reload; Stop settled at 180; Resume continued to 380 and beyond. Page two had 50 distinct rows with no overlap with page one. The submenu alias and 390px layout passed.
• Anonymous live requests were rejected; nonce/capability failures, lease handling, 120-result pagination, visibility, authorization expiry, and late/failed Stop responses have regression coverage.
• All 147 deployed runtime files matched the ZIP. All 19 module option arrays and 1,203 existing post/page content/type/status hashes matched the snapshot.
• Earlier module QA covered native duplication, real link checks, CSV export, activity filtering, all 19 backend pages, dense phone layouts, and light/dark admin mark previews.

Link Health covers stored anchor links in published public posts/pages, up to 1,000 unique links per post. Dynamic output and password-protected content are excluded. Hidden/closed workspaces rely on the site's background scheduler. The existing Fonts/Components/SVG editor-iframe visual gate is tracked for a later public release; this PR is ready to merge.

Verification and recovery: docs/v1.7.0-verification.md, docs/ui-polish-verification.md, docs/ui-sidebar-verification.md, docs/link-health-live-verification.md, and docs/branding-assets.md.