* fix(landing): scope landing route to always-light palette
The landing page sections use hardcoded light colors (bg-white / #0a0d12),
but shared components rendered inside — notably CloudWaitlistExpand on
/download — use semantic tokens that flip to dark values under next-themes'
`.dark` class, producing a mismatched dark card on an otherwise light page
when the user's OS is in dark mode.
Add a `.landing-light` class on the landing layout wrapper that re-declares
all color tokens to their light values for the subtree, so nested
token-driven components stay in lockstep with the hardcoded palette.
* test(agent): serialize fake-executable writes to avoid ETXTBSY on CI
TestKimiBackendInvokesACPSubcommand (and its Kimi/Codex siblings) write a
shell script to a per-test TempDir and then fork/exec it. With t.Parallel()
enabled across the package, a concurrent goroutine's fork can inherit the
still-open write fd to another test's new executable; Linux then rejects
the subsequent exec with ETXTBSY (seen as
fork/exec /tmp/.../kimi: text file busy
on GitHub Actions).
Introduce writeTestExecutable, which holds syscall.ForkLock.RLock across
OpenFile→Write→Close. Fork (which takes ForkLock.Lock) cannot run while we
hold RLock, so no sibling fork inherits our write fd. Ran the three callers
with -count=10 under -p=1 and the full package with no failures.
