Add browser-level tests for the dispatch cockpit surfaces (incl. the unverified cross-project nesting)

[pat-lewczuk]

Follow-up from #972

#972 added the dispatch cockpit surfaces — the composer's Dispatch toggle and its limits popover/sheet, dispatched children nested under their parent in three task lists, and the run-header parent/subtasks panels. packages/web/e2e/ holds 30+ browser specs and none was touched, so these surfaces are pinned only by unit tests.

UI QA drove the whole scenario by hand and it passed (evidence, 11 screenshots); this issue is to turn that manual pass into a spec. The ready-to-implement scenario is written up in the follow-up comment — fixtures, assertions and teardown.

One surface stayed unverified even by hand: the cross-project "All tasks" list. QA could not reach it because the throwaway CEZ_HOME has an empty project registry and the cockpit rightly refuses to register a cezar task worktree as a project. A two-project fixture closes that gap, which makes this the one nesting surface that has never been seen working.

Acceptance criteria

• A runs.json fixture with a root (dispatch.intent) and two children (dispatch.parentRunId, kinds implement and review), in a throwaway dataRoot per the fixtureServeEnv pattern.
• Project table: children carry data-depth="1", follow their parent row directly, parent cell reads 2 subtasks, kind chips render.
• Cross-project list: same nesting, with a two-registered-project fixture.
• Sidebar quick-list: nesting within a state group, and the documented top-level fallback when the parent sits in another group.
• Run header: a child links to its parent; the parent lists its subtasks.
• Composer: the toggle forces Worktree on+disabled and auto-checks Autonomous; the chevron opens the limits popover; In flight at once offers nothing above 4.
• Regression: with CEZ_DISPATCH=0 no dispatch control renders and the "Review open PRs" template is absent.
• Teardown deletes the dataRoot and every fixture.

Related: #972