test(cypress): give server round trips room in the specs that wait on them

[joewiz]

[This PR was prompted by Joe, drafted by Claude Code, and reviewed by Joe.]

Problem

Several assertions wait on a server round trip while using Cypress's 4-second default (or a hand-set 5 seconds). That is comfortable on a warm instance and tight on a loaded CI runner or a freshly started container, so these specs fail intermittently and are then hard to distinguish from real regressions — which is exactly what made the reports in #821 so hard to act on.

Three sightings, all of which passed on an immediate re-run:

spec	assertion	where
autocomplete_spec	.cm-tooltip-autocomplete after "shows repo: completions when typing repo without colon"	#865's first CI run
apply_configuration	save dialog closed, first save against a cold container	local full-suite run
websocket_spec	diagnostics push after compile	local full-suite run

The autocomplete one also appears in the failure tables reported in #821.

Change

Raise the timeout only on assertions that are waiting on the server, and say so in a comment where it is not obvious:

• 10s — the completion popup (served by the language service), the save dialog opening and closing, the "stored" / "Configuration applied." toasts, and the path label after a save
• 15s — websocket_spec's diagnostics assertion, which waits for a compile request and a push back over the socket

Assertions that only wait on local DOM work are left at their existing values; this is not a blanket bump.

Verification

Full suite on the stack the eXist-db image bundles (eXist-db 7.0.0-SNAPSHOT, existdb-openapi 0.10.0, Roaster 1.12.2), clean container: the three specs above pass, and the suite is otherwise unchanged from develop.

[duncdrum]

There are two leaner option:

• adjust the default timeouts in cypress config, instead of per testcase
• configure retries in cypress configs (this works really well in my experience) to get rid of more flake

The third option (most work but best results):
Where possible make longer chains using cy.request with assertions on outgoing and request and incoming responses, where each one starts a new timeout window, and failures become much more informative