feat(ui): sidebar groups, dock editor, worklist rows [no-ticket]

[matthias-scale]

Supersedes #38. The original PR head could not be changed through GitHub's pull-request API, so this repaired head is submitted as a replacement.

Summary

• carries the sidebar grouping and pinning, dock/editor, and compact worklist-row UI commits from the split onto the current fork/pr-base
• retains the UI slice only; detect and closing-block contract changes already present in the base were removed by the normal rebase
• repairs current-base API and default-keymap compatibility so the branch is green
• removes the obsolete v1 demo/ duplicate; canonical payload-v2 closing-block assets remain under src/integration/assets/closing-block/

Rebase

• base: 4f82ffc18ff3cca4d41381b4eb856b05b53ae1d8
• source: 725cf298d03b7c353b57e4d1704aed1e22e98010
• the UI implementation commits and the two original empty provenance commits are preserved
• detect, contract, and stale demo commits whose patch contents were already upstream became empty during the normal rebase; no non-upstream commit was skipped

Validation

• just check-parallel passes all six lanes: lint, Rust/nextest, Windows lint, maintenance, integrations, and marketplace
• focused dock-editor, terminal-attach, multi-client, geometry, reload-config, schema, and live-handoff tests pass
• validation used disposable XDG config/state/cache and Cargo homes; no daily-driver Herdr state was touched

AC5/AC6 repair evidence

• AC5 ✓ server::headless::tests::full_app_background_client_does_not_resize_shared_dock_editor_runtime renders two attached full-app clients with different viewports (100x30, dock 24) and (160x45, dock 48), both with the editor dock open. Red-first at the prior head printed before=(2, 10), after=(28, 22), proving the background client resized the shared editor PTY. On the repaired head, the test records exactly one resize, owned by the foreground client.
• AC5 ✓ dock geometry remains client presentation/layout state: each render uses that client's DockPresentationState and view geometry, while the shared editor PTY is sized only from the foreground client's layout. The six obsolete crate::ui::dock forwarding aliases were removed; server cursor projection remains on the neutral src/server/render_stream.rs surface.
• AC6 ✓ handle_tab_pin returns structured tab_not_found when tab projection returns None; api_tab_pin_projection_divergence_returns_structured_error exercises that divergent-invariant path. mobile_switcher_target_for_row returns None for section headers instead of unreachable!; mobile_switcher_section_header_is_non_panicking covers it.
• AC6 ✓ api_tab_pin_toggle_flips_pinned_flag and mobile_switcher focused suites remain green.

Repair commits:

• 473d45459dec5816467fbe3f542967b4fe29e514 — fix shared dock editor resize ownership for divergent full-app clients
• 5c67ba2f4206bbd770a443cdd74976f7879bdd28 — AC5 boundary split
• f6228ccc5a4553882da849104c6647da3b2c7751 — AC6 panic removal
• df4f6a3f317e3162935f1fd65ae8a89f0f45197b — remove misleading dock-editor forwarding aliases and track AC5 ownership deferral