refactor(ui): extract non-chat component groups

[Astro-Han]

Summary

Extracts the non-chat dependency groups from packages/ui/src/components.tsx into focused sibling modules while keeping the public @maka/ui surface stable through components.tsx re-exports.

Move map:

• nav-selection.ts: NavSelection / SessionFilter
• modal-a11y.ts: useModalA11y
• tool-format.ts: tool formatting helpers
• empty-state.tsx: EmptyState
• capability-audit-strip.tsx: CapabilityAuditStrip
• search-modal.tsx: SearchModal
• session-list-panel.tsx: SessionListPanel + row/group helpers
• tool-activity.tsx: ToolActivity, OverlayHost, preview surfaces, formatBytes
• permission-dialog.tsx: PermissionDialog + permission summary helpers
• module-panel-types.ts: shared sidebar/module panel types

Why

Refs #363. This is PR2 from the sink-file split plan: cut unrelated non-chat UI responsibilities out of components.tsx without changing runtime behavior or visual output.

Scope

Changed:

• Added focused packages/ui/src/* sibling modules for the extracted non-chat groups.
• Kept components.tsx as the compatibility re-export point, so packages/ui/src/index.ts and existing consumers continue to work.
• Moved toast.tsx to import useModalA11y from the leaf module to avoid a components.js back-edge.
• Co-migrated source-reading contract tests to the new file paths.

Not included:

• No ChatView, Composer, Settings, main.tsx, Storybook, CSS, or visual redesign work.
• No new dependency or CI import-cycle tooling.

Verification

• npm run -w @maka/ui build
• npm run -w @maka/desktop build:main
• npm run -w @maka/desktop typecheck
• npm run -w @maka/desktop build
• node scripts/check-a11y.mjs
• npm run build
• Targeted desktop contract set: 216 tests passed, 0 failed

Known unrelated blocker:

• npm run -w @maka/desktop test currently stops in pretest on the existing check-console gate for packages/headless/src/harbor-cli.ts console calls.

User-facing impact

None expected. This is intended to be behavior- and visually-neutral. No CHANGELOG.md, docs, breaking changes, or migrations.

Reviewer notes

Cycle guard checked the new UI leaf files for imports from @maka/ui, ./index.js, or ./components.js; no matches. components.tsx still re-exports the moved declarations so the public API remains intact until the later chat extraction slice.