feat(macOS): add native title-bar navigation and sidebar controls

[kshivang]

Description

Adds native macOS title-bar controls for the sidebar, Space selection/rename, browser navigation, search, and existing host actions. The collapsed sidebar no longer leaves a vertical strip; its floating panel respects the top bar and update banner. Browser tabs share their address, favicon, autocomplete, suggestions, navigation and copy-link actions with the native title bar, and hide their in-tab toolbar while hosted.

Platform scope

The new title bar is macOS-only. usesNativeSidebarTitleBar gates integration by OS and sidebar placement, SidebarTitleBar retains the existing non-macOS branch, and the desktop native bridge independently refuses non-macOS windows. Windows/Linux retain their existing title bar and in-browser toolbar. Regression coverage checks every sidebar placement on non-macOS.

Other requested changes in this PR are shared: compact oval pane tabs with hover close and full-tab ripple, strip-relative context menus, split creation, heavyweight drag targets, improved favicon reuse, bounded partial filename search results, and an opt-in Last Session setting (off by default) that preserves restoration of the last known Space.

Type and version impact

• New feature and bug fixes
• Tests and documentation
• Minor feature impact; host version remains managed by release automation

Validation

• Full host desktop suite: 7,065 tests, zero failures/errors, five skipped; API contract module: 10 tests passed.
• Host ktlint and detekt passed.
• API dependency: full build, ABI check, and 124 tests passed.
• Browser dependency: 536 tests and plugin JAR build passed.
• Full host suite preceded the final owner-aware focus-cleanup fix; focused bridge/platform tests and API contract checks also passed on the final head, along with compilation, ktlint and detekt.
• macOS preview was iterated during development. Windows/Linux runtime checks and packaged distributions have not been run locally; their gating was reviewed and regression-tested.
• API 1.0.94 is published; the host API contract checks also pass against its downloaded release JAR. Shared API-module formatting and static analysis now pass locally.

Dependencies and merge order

1. Done: feat(browser): add optional native title-bar bridge boss-plugin-api#64 merged and API 1.0.94 published. The host pins this release.
2. Done: feat(browser): support optional native title-bar navigation boss-plugin-fluck-browser#47 merged and browser 1.2.31 published, built against API 1.0.94.
3. Rerun host CI against the published API, then merge this PR after review.

Separate BossTerm fullscreen appearance fix: kshivang/BossTerm#435.

Review focus

• AppKit window/toolbar ownership, fullscreen appearance, and native URL field focus lifecycle.
• Sidebar placement with left plugins, top bar, update banner, and collapsed state.
• Windows/Linux fallback and optional browser bridge behavior.
• Space restoration without a synthetic Last Session by default.

Pre-merge checklist

• Self-review and platform-gate audit
• Unrelated settings work excluded from this branch
• API 1.0.94 published and browser 1.2.31 released
• Required CI and review complete
• Windows/Linux runtime smoke checks

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