[flexdinesh]

• Navigation owns one resizable frame for Diff and Repos, in that order. Both views share saved width, pointer/keyboard resizing and collapse behavior; selecting a stream opens its diff and file tree.
• Replace inline project search with the Repos magnifier opening the existing review picker. Preserve review state, mobile drawer focus, loading/error recovery and local/remote behavior.
• Tighten the header to the 36px desktop rhythm, center mixed UI/monospace text by font metrics, and anchor the 16px Theme control to the shell’s right edge independently of diff scrollbars. Remove snapshot deletion from the header.
• Update canonical design/system documentation and behavior checks. Keep API deletion and review persistence contracts unchanged; remove obsolete tests for the intentionally removed header action.
• Validation: CI/build/type/lint/format/API checks, architecture/design/shared contracts, unit/release tests and complete Go/race suites passed. The 82-case browser run passed 81 cases; its hot-reload-interrupted case passed separately. Focused header, native-scrollbar, shared-resize, Repos and mobile regressions pass, including the added centering test. Manual polish covered light/dark desktop, tablet, mobile, enlarged text and long labels; Repos accessibility scan reports zero violations.
• Validation caveat: a transient existing hook-worker temporary-directory cleanup failure passed on the complete Go rerun.