Redesign AppKit sidebar groups and live reordering - #9446

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@cmuxTests/SidebarAppKitRowCellTests.swift`:
- Around line 353-383: Extend workspaceTitleRendersMarkdownWithRegularBaseWeight
and workspaceDescriptionPreservesMarkdownFontTraits to assert both rendered
strings exclude Markdown delimiters and both fields use the required 12.5-point
base font. Reuse the existing font inspection helpers where applicable, while
preserving the current bold, italic, and regular-trait assertions.
- Around line 385-400: The test
unreadBadgeExpandsForLargeCountsAndKeepsFullAccessibleCount only covers the
plural unread-count branch. Add a separate count-1 case using
Self.configuredCell and assert the badge’s accessibilityLabel() uses the
singular ICU .one localization value, while retaining the existing 125-count
.other assertion.

In
`@Packages/macOS/CmuxSettingsUI/Sources/CmuxSettingsUI/Sections/SidebarSection.swift`:
- Line 16: Make the `@State` property workspaceSpacing private to satisfy SwiftUI
state encapsulation. Update workspaceSpacingRow in
SidebarSection+WorkspaceSpacing.swift by moving it into SidebarSection.swift or
extracting a separate row view that receives a Binding, preserving its current
behavior while avoiding direct access to the private state.

In `@Resources/Localizable.xcstrings`:
- Around line 190620-190636: Complete localization coverage in
Resources/Localizable.xcstrings for the three workspace-spacing keys:
settings.search.alias.setting.sidebarAppearance.workspace-spacing at lines
190620-190636, settings.sidebarAppearance.workspaceSpacing at lines
194985-195018, and settings.sidebarAppearance.workspaceSpacing.subtitle. Add
translated values for every locale currently supported, preserving the existing
English and Japanese entries.

In `@Sources/Sidebar/AppKitList/Cells/SidebarWorkspaceRowCellView.swift`:
- Around line 443-450: Remove the DEBUG-only diagnostic in the title-paint path
that logs displayTitle from the sidebar row cell. If retaining a diagnostic is
necessary, replace the raw workspace title with non-sensitive metadata such as
its byte count, while preserving the existing mismatch check and avoiding any
user-controlled title content.
- Around line 618-621: Update the unread accessibility label construction near
model.unreadCount to select explicit ICU-style .one and .other localization keys
based on whether the count equals one or not, instead of using
String.localizedStringWithFormat. Add matching catalog entries for both keys
with locale-appropriate singular and plural wording.

In `@web/data/cmux.schema.json`:
- Around line 1047-1054: Add non-empty localized entries for
schemaDescriptions.sidebar.workspaceSpacing in the sidebar sections of
web/messages/en.json and web/messages/ja.json, matching the existing message
structure so the referenced schema description resolves in both locales.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Duplicate comments:
In `@Resources/Localizable.xcstrings`:
- Around line 190620-190636: Complete localization coverage for the three
workspace-spacing keys: Resources/Localizable.xcstrings lines 190620-190636
requires translated entries for every supported locale for
settings.search.alias.setting.sidebarAppearance.workspace-spacing; lines
194985-195018 likewise require every supported locale for
settings.sidebarAppearance.workspaceSpacing and
settings.sidebarAppearance.workspaceSpacing.subtitle. Preserve the existing
English and Japanese entries while adding appropriate translations for all
remaining supported locales.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@cmuxTests/SidebarAppKitRowCellTests.swift`:
- Around line 454-480: Update groupPinAlignsWithWorkspacePin to convert both pin
origins into their enclosing cell coordinate spaces before comparing horizontal
positions; compare the converted minX values rather than the raw frame.minX
values, while preserving the existing pin discovery and alignment assertion.
- Around line 428-452: Update
groupHeaderUsesMarkdownRegularWorkspaceSizedTextWithoutFolderIcon to inspect
every attributed font run in the group-name NSTextField, rather than relying
only on name.font. Assert that each run’s font has a 12.5-point size while
preserving the existing bold, italic, plain-run, text, and icon assertions.