Add regression coverage for single client connection inventory

## Problem
The current test suite does not cover single client connection inventory.

## Expected behavior
- A focused Vitest case locks the existing behavior.
- The targeted test file passes and fails if the covered behavior regresses.

## Scope
Only add regression coverage for $(@{Slug=client-single-connection; Focus=single client connection inventory; PrTitle=test(client-connections): cover a single connection inventory; TestFile=web/src/utils/clientConnectionDiagnostics.test.ts; Mode=existing; Append=describe('client connection diagnostics single connection', () => {
it('reports a single producer connection with stable summary counts', () => {
const diagnostics = analyzeClientConnections([connection({})]);

expect(diagnostics.summary.totalConnections).toBe(1);
expect(diagnostics.summary.uniqueClientCount).toBe(1);
expect(diagnostics.resources).toHaveLength(1);
});
});}.TestFile). No runtime behavior changes.

## Acceptance criteria
- [ ] The targeted Vitest file passes.
- [ ] git diff --check is clean.

Start with web/src/utils/clientConnectionDiagnostics.test.ts and inspect the existing client connection diagnostics tests and helpers. Run the targeted Vitest file, then add coverage for one connection with the specified summary counts and resource length. Done means the targeted file passes and git diff --check is clean.

Written by the indexing model from the issue text.