test(web): stop MessagesTimeline tests silently skipping under load

[incognitojam]

Problem

MessagesTimeline.test.tsx needs DOM globals stubbed before its module graph is
evaluated, because the web unit project runs on the node environment. It
did that by deferring the import into a hook:

let MessagesTimeline: typeof import("./MessagesTimeline").MessagesTimeline;

beforeAll(async () => {
  vi.stubGlobal("window", { /* ... */ });
  ({ MessagesTimeline } = await import("./MessagesTimeline"));
}, 30_000);

That puts the module graph's transform cost inside a hook timeout. Run alone
the file takes 3s, but under full-suite contention the hook hit its 30s timeout
and the file reported 18 tests | 18 skipped at 30100ms — without failing.
CI stayed green having run 18 fewer tests than it appeared to.

This is pre-existing, but #112 moved Fork Test to a 4-core free runner, which
makes the contention that triggers it more likely.

Fix

Move the stubs into vi.hoisted, which runs ahead of imports, so
MessagesTimeline is imported statically and no hook timeout wraps the module
graph. This removes the failure mode structurally rather than by raising the
timeout. vi.hoisted is already the idiom in ~10 other web test files.

Verification

• File alone: 18/18 pass.
• Timing confirms the cost moved out of the hook phase: tests 2.62s / import 619ms before, tests 98ms / import 2.16s after. No hook timeout
  applies to the import phase.
• Full @t3tools/web suite: 250 files / 2451 tests, 0 skipped, exit 0.
  Previously this run showed MessagesTimeline at 18 tests | 18 skipped.
• @t3tools/web typecheck clean.

Worth noting the original stall was intermittent (1 of 2 full runs), so a green
run is not by itself proof. The argument for the fix is structural: there is no
longer a timed hook around the import.

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Written by an agent (Claude Code, claude-opus-5).