test(host-environment): cover laptop/desktop, platform, display, timezone predicates

Four new test files extending the existing test-host-environment.el
(which already covered the two battery helpers).

- platform-predicates: env-linux-p, env-bsd-p, env-macos-p, env-windows-p
  walked across every supported system-type value. 8 tests.
- display-predicates: env-x-p, env-x11-p, env-wayland-p, env-terminal-p,
  env-gui-p exercised under every relevant combination of window-system,
  WAYLAND_DISPLAY, and display-graphic-p. 13 tests.
- env-laptop-p: composition over the helpers, with Linux dispatch
  isolated from non-Linux dispatch via system-type binding. 8 tests
  including env-desktop-p as the inverse. battery-status-function is
  forward-declared in this test file (initialized to nil) so cl-letf's
  symbol-value place can read the prior value without hitting
  void-variable.
- detect-system-timezone: the four-method priority chain. Mocks
  cj/match-localtime-to-zoneinfo and getenv at the boundary; uses
  cl-letf on file-exists-p / insert-file-contents to exercise the
  /etc/timezone fall-through without touching real system files.
  5 tests.

34 new tests for host-environment, all passing. Full suite green.

0 files changed, 0 insertions, 0 deletions