feat: hide unchanged files when comparing metadata between orgs

[paustint]

When comparing metadata across two orgs, the sidebar colors every file green or red, but a retrieve routinely returns hundreds or thousands of components and nearly all of them match. The handful of differences the user opened the modal to find are buried, and the tree had no filter of any kind.

Closes #1334

[Copilot]

Pull request overview

This PR improves the “compare metadata between orgs” experience by adding an option to hide unchanged (matching) metadata files so users can focus on the small set of differences, addressing the usability problem described in #1334.

Changes:

• Added a “Hide Unchanged Files” toggle in the metadata comparison sidebar, including a visible/total file count and an empty-state message when everything matches.
• Introduced tree filtering/counting utilities to remove matching files while pruning empty folders.
• Improved the shared Tree component so that when its items list changes and the selected node disappears (e.g. due to filtering), it selects and emits the first remaining leaf node; added tests and Vitest DOM setup for the deploy feature.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
libs/ui/src/lib/tree/Tree.tsx	Adds fallback selection behavior when the selected tree item is filtered out.
libs/ui/src/lib/tree/tests/Tree.spec.tsx	Adds coverage for re-emitting selection and fallback selection behavior.
libs/features/deploy/vite.config.mts	Adds shared DOM test setup to support new UI tests.
libs/features/deploy/src/view-or-compare-metadata/viewOrCompareMetadataUtils.tsx	Adds filterUnchangedFiles and countMetadataFiles helpers for the sidebar filter.
libs/features/deploy/src/view-or-compare-metadata/ViewOrCompareMetadataSidebar.tsx	Adds the “Hide Unchanged Files” toggle, file counts, and empty-state messaging; uses filtered tree items.
libs/features/deploy/src/view-or-compare-metadata/ViewOrCompareMetadataModal.tsx	Adds label help text for “Hide Unchanged Regions”.
libs/features/deploy/src/view-or-compare-metadata/tests/viewOrCompareMetadataUtils.spec.ts	Adds unit tests for filtering and counting utilities.
libs/features/deploy/src/view-or-compare-metadata/tests/ViewOrCompareMetadataSidebar.spec.tsx	Adds sidebar behavior tests for filtering, counts, and selection behavior.

Suppressed comments (1)

libs/ui/src/lib/tree/Tree.tsx:88

• Typo in inline comment: "e.x." should be "e.g." ("for example").

      // The selected item is no longer in the tree (e.x. it was filtered out), fall back to the first remaining leaf node.
      // Updating the selection re-runs this effect, which is what emits the new selection.
      const firstLeafNode = getFirstLeafNodeId(ids, idMap);

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[paustint]

Code review summary

Automated review (Claude Code). Fixes below are pushed as an amend to the PR head.

Verdict: clean, well-scoped display-time filter with solid unit coverage. No outstanding decisions.

Verified correct: the filter is non-mutating and memoized, and the deploy/export/footer counts correctly continue to use the unfiltered set.

Fixed and pushed

• viewOrCompareMetadataUtils.tsx — a real diff could be silently hidden. Two nullish contents compared as equal, so a file whose content could not be read from the retrieve zip on both sides was classified "unchanged" and vanished entirely once the filter was on. That is the dangerous direction for this feature: indistinguishable from "identical". Files are now retained when either side's content is nullish, since equality is unknown rather than proven. Test added for the both-nullish case.
• useViewOrCompareMetadata.tsx — stale error hid the new toggle. The reducer never cleared targetError, so once a target fetch failed the error persisted and permanently hid the toggle even after a successful retry. FETCH now clears the error per-branch.

Before applying the second fix, confirmed it masks nothing: FETCH already resets loading/status/results for the org being fetched, FETCH_ERROR is the only writer of these fields, and nothing reads the error after a new fetch begins. Clearing is per-branch because handleReload re-fetches both orgs and targetError cannot be set before a target org is chosen.

(features-deploy 18/18, Tree.spec.tsx 16/16, typecheck clean.)

Note: the fix lives in the hook, not ViewOrCompareMetadataSidebar.tsx — the sidebar only consumes props.