Structured diff for JSON/block changes in the change view

[KevinJump]

Summary

• Replace the word-diffed, pretty-printed JSON in the change-detail view with a structured diff: each USyncChange is classified (masked, single-sided, JSON, XML/text lines, word, scalar) and rendered with the strategy that suits it, instead of running every value through diffWords.
• JSON/block values get a recursive leaf-change walk that matches array elements by identity (key/udi/alias+culture, with a fallback to index matching) so inserting one block in a block list reports one change, not a rewrite of the whole array.
• Long text/XML gets a hand-rolled line diff (Umbraco only re-exports diffWords, so no new dependency) with collapsed unchanged runs.
• The uui-table is replaced with a list of expandable rows so the diff gets the full width of the sidebar modal. A row starts open when it's the only change and collapsed once there's more than one; a failed (success: false) detail always forces itself open. Each JSON row has a "show raw values" toggle for the full old/new text.
• Fixes two accidental-precedence bugs (length ?? 0 > 0 parses as length ?? (0 > 0)) and a case where Error/Warning notice details were being word-diffed against '' instead of shown as a message.

All diff logic lives in dependency-free modules under src/utils/diff/ (no imports from Lit or @umbraco-cms/*), so it can be exercised outside the backoffice; the identity-matching heuristic, JSON-string expansion, and line-diff bail-out behaviour were checked against fixtures in a throwaway harness before wiring up the component.

Test plan

• npm run typescript:build — clean
• npm run build — succeeds
• npx prettier --check on all changed files
• In the backoffice: block list with one block inserted → one change reported, not a full rewrite
• Block reorder only → reorder notice, no/few leaf changes
• Culture-variant property → culture tag shown, not baked into the name
• Masked value (member/user) → never diffed, shown as hidden
• A failed import with error/warning details → notice shown, row open by default
• Dark mode

🤖 Generated with Claude Code