#20498: UI: modularize control UI architecture and normalize spacing.

## Summary - Problem: `ui/src/ui` and `ui/src/styles` were tightly coupled (loose root files + monolithic CSS), making maintenance harder. - Why it matters: higher risk of layout/style regressions and expensive refactors/reviews. - What changed: - Modularized `ui/src/ui` by domain: `app`, `core`, `lib`, `models`, `navigation`, `theme`, `tools`, `usage`, `identity`. - Updated imports/paths and entrypoint (`ui/src/main.ts` -> `./ui/app/app.ts`). - Modularized styles and normalized spacing with `--space-*` tokens across `ui/src/styles/**`. - What did NOT change (scope boundary): no gateway/backend/API/contract changes. ## Change Type (select all) - [ ] Bug fix - [ ] Feature - [x] Refactor - [ ] Docs - [ ] Security hardening - [ ] Chore/infra ## Scope (select all touched areas) - [ ] Gateway / orchestration - [ ] Skills / tool execution - [ ] Auth / tokens - [ ] Memory / storage - [ ] Integrations - [ ] API / contracts - [x] UI / DX - [ ] CI/CD / infra ## Linked Issue/PR - Closes #N/A - Related #N/A ## User-visible / Behavior Changes - More consistent UI spacing. - No intended functional behavior changes. ## Security Impact (required) - New permissions/capabilities? (`No`) - Secrets/tokens handling changed? (`No`) - New/changed network calls? (`No`) - Command/tool execution surface changed? (`No`) - Data access scope changed? (`No`) - If any `Yes`, explain risk + mitigation: `N/A` ## Repro + Verification ### Environment - OS: Windows - Runtime/container: Node + pnpm - Model/provider: N/A - Integration/channel (if any): N/A - Relevant config (redacted): N/A ### Steps 1. `pnpm format:check` 2. `pnpm ui:build` 3. `pnpm test:ui` (optional) ### Expected - UI build succeeds and import/path resolution is valid. - Styles compile without errors. ### Actual - `pnpm format:check` ✅ - `pnpm ui:build` ✅ - `pnpm test:ui` ✅ ## Evidence - [x] Trace/log snippets - [ ] Failing test/log before + passing after - [ ] Screenshot/recording - [ ] Perf numbers (if relevant) ## Human Verification (required) - Verified scenarios: UI build, import resolution after file moves, formatting checks. - Edge cases checked: relative paths between moved modules and stylesheet loading. - What you did **not** verify:NA ## Compatibility / Migration - Backward compatible? (`Yes`) - Config/env changes? (`No`) - Migration needed? (`No`) - If yes, exact upgrade steps: `N/A` ## Failure Recovery (if this breaks) - How to disable/revert this change quickly: revert this PR. - Files/config to restore: `ui/src/ui/**`, `ui/src/styles/**`, `ui/src/main.ts`. - Known bad symptoms reviewers should watch for: broken views, unresolved imports, missing styles. ## Risks and Mitigations - Risk: visual regression from spacing normalization. - Mitigation: consistent tokenization + validated build. - Risk: broken paths after file moves. - Mitigation: global import rewrite + validated build.