Remove timing assumptions from UI and HTTP tests

[lukebuehler]

UI tests could pass on a PR and fail on main because they assumed file loading, uploads, or focus changes would finish within a fixed sleep. Replace those assumptions with assertions that wait for the required state.

• Wait explicitly for workspace editors, upload outcomes, blob views, file references, and dictation uploads; control workspace tree and file responses with deferred promises.
• Use fake timers for menu focus and demo event completion, and clear query clients between tests.
• Synchronize the MCP disconnect test with upstream request startup before aborting.

Validation passed locally:

• npm run check
• Three shuffled runs of the complete web suite: 806 tests per run, two workers, seeds 101/202/303.
• Three additional shuffled runs of the final affected web suites: 182 tests per run, two workers, seeds 101/202/303.
• Configurator HTTP suite: 8 tests.
• git diff --check