* Add branch line total chip to source control header
Display the total lines added and removed across a branch from its fork point, measured via `git diff <mergeBase>`. Only computed when the chip is visible (request gate on merge base OID), with 500ms soft deadline to protect status latency and 15s hard timeout. Deduplicated across concurrent pollers and cached alongside line stats. Omitted on failure — always shows exact or nothing, never a partial estimate. Updates throughout the stack: native git status, relay, renderer store/API, and UI components.
* Pin branch line total to app locale
Format line counts using the app's configured locale instead of the system
locale, ensuring consistent cross-platform display and test reliability.
* test: wait for coalescer joins instead of fixed sleep
Hold the diff until the second status pass actually takes the
branch-total coalescer lease instead of using a fixed 400ms sleep.
Fixes timing-dependent flakiness on slow machines.
