feat(knowledge): move folders with drag and drop or actions menu

[Annabelle0726]

Description

Add two ways to change a knowledge folder's parent: drag it onto another folder (or the knowledge-base root), or use Actions → Move to folder. Both reuse the existing folder move endpoint and preserve the folder name, descendants, selected path and recursive document counts.

• Exclude self/descendant, unchanged, duplicate and stale destinations; disable mutations for read-only users and while a move is pending.
• Offer focusable menu buttons, Escape-to-trigger focus restoration and a touch-accessible alternative to dragging.
• Validate every descendant's resulting path before the repository writes any rows. Previously, normalization could silently truncate an over-deep moved subtree.
• Add the new labels to the existing six locales.
• Repair a missing useConnectorLabel mock in the existing assistant-refresh test fixture, which otherwise prevents the current upstream frontend suite from passing.

Type of Change

• ✨ New feature
• 🐛 Bug fix
• 🧪 Test

Testing

• npm test: 1,800 passed, 0 failed, 1 existing skip.
• npm run type-check: passed.
• NODE_OPTIONS=--max-old-space-size=4096 npm run build: passed; existing large-chunk warnings only.
• Focused folder/component tests: 12 passed.
• go test ./internal/application/repository: passed, including the regression that fails on unmodified upstream.
• go vet ./... and go build ./cmd/server: passed on this branch.
• golangci-lint v2.12.2, filtered with this PR's patch and scoped to ./internal/application/repository: 0 issues, successful exit.

Checks used Linux Go 1.26.9 and Node 24. Upstream GitHub Actions currently require maintainer approval (action_required); remote CI has not run yet.

Browser verification used Chromium and an isolated API fixture: drag/reparent, move to root, subtree preservation after refresh, menu/keyboard operation, Escape focus restoration, rejected cycles, failed requests retaining the original tree, and read-only permissions. The move menu was checked at 1920, 683 and 390 px. The existing workspace minimum-width layout still requires horizontal scrolling at 390 px; this PR does not redesign that layout.

Checklist

• git diff --check upstream/main...HEAD passes
• Changed source files are formatted
• Targeted tests for the changed packages/components pass
• Diff-scoped Go lint passes
• Full-repository checks were run; results are recorded above
• Self-reviewed the code
• Added regression tests
• No breaking API or migration changes

Screenshots