* feat(web): add collapsible sections to changes panel
Sections (Unstaged, Staged, Commits, PR Changes, PR Commits) can now
be collapsed/expanded by clicking the section header or chevron arrow.
Includes Playwright E2E test validating collapse and expand behavior.
* fix(web): add aria-expanded to collapsible section toggles
Addresses CodeRabbit review: adds aria-expanded attribute to section
toggle buttons for screen reader support, and asserts the attribute
in the E2E test.
* fix(web): render section toggle as button only when collapsible
Non-collapsible sections keep a plain <span> label to avoid
ambiguous getByRole("button") matches in E2E tests (e.g. "Commit"
action button vs "Commits (0)" section header).
* fix(web): use exact match for Commit button in pre-hooks E2E test
The collapsible "Commits" section toggle button now matches
getByRole("button", { name: "Commit" }) via substring. Use exact
matching to only target the action button.
José Almeida