refactor(component-ownership): relocate misplaced shared components

[Harry19081]

Problem

App-root services, engine-owned terminal/session UI, domain-specific tables and hover cards, and reusable primitives had accumulated under generic component/shared roots. That obscured ownership, encouraged broad forwarding barrels, and made import direction difficult to reason about. The terminal relocation also exposed two concrete hazards: stale relative Sass paths and a reverse TerminalCore-to-SessionCore composition dependency.

Solution

• Relocate app-shell services and root components under app/root, engine-specific terminal and replay components under TerminalCore and SessionCore, and domain components beside their owning modules.
• Move genuinely neutral primitives such as Placeholder, tab-pill controls, header separators, toolbar tooltip, and settings search into reusable component homes.
• Preserve the current terminal accent/cursor behavior and lazy loading, fix relocated stylesheet paths, and let chat/workstation hosts compose the SessionCore read-only renderer into TerminalCore.
• Remove obsolete forwarding barrels and unused reexports; retain only intentional entry points with live consumers.
• Keep stable ModelTable contracts and shared constants in neutral type/config modules while moving its implementation to KeyVault ownership.
• Update active documentation and startup dependency guards for the new paths.

Potential risks

The primary risk is import-path churn across a large internal surface: downstream branches or untracked local code that still imports the retired paths will need to update. Terminal chunking, CSS resolution, theme repainting, and read-only composition are the highest runtime-risk areas; targeted tests and a production webpack build cover them. No dependency, lockfile, persistence, schema, IPC, wire-format, or public package API changes are included. Rollback is a single-commit revert.

No screenshots were captured because this is an ownership/import refactor with no intended visual change; screenshots would not distinguish the result. A desktop GUI smoke test was not run because Computer Use was not authorized.

Verification

• npm run typecheck — passed on the committed tree
• npm run lint — passed; commit-time lint-staged also passed for 412 source files
• npm run check:circular — passed; no cycles across 6,546 modules
• npm run build — passed; production webpack bundle compiled
• npx vitest run src/app/root/components/ErrorBoundary/index.test.ts src/components/Placeholder/normalizePlaceholderSubtitle.test.ts src/components/TabPill/config.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/FileTreeContent/tests/treeUtils.test.ts src/engines/ChatPanel/ChatPanelTabBar/ChatPanelTabBar.test.ts — 5 files / 36 tests passed
• Terminal-focused Vitest sweep covering TerminalCore, TerminalReadOnly, TerminalBlock, TerminalMainContent, startup graph, terminal stores/services/hooks, CLI session bridge, replay bridge, and terminal utilities — 34 files / 287 tests passed
• git diff --check origin/develop...HEAD — passed
• Legacy root/import sweep — no live source imports or files remain at the retired component paths
• Export review — only FileTreeContentHandle and ResizableSplitPanel are newly forwarded, and both have live consumers

The focused frontend consistency review was applied manually because the documented frontend-ui-audit skill is unavailable in this workspace. No new design-system, accessibility, arbitrary-value, or visual-pattern concerns were found.