fix(channels): cancel deferred color-swatch focus (port of upstream #1945)

[adminopenclaw8-sketch]

Summary

• retain the deferred initial focus used for keyboard accessibility
• cancel stale focus timers when the picker closes or reopens
• avoid stealing focus after the user has already navigated to another swatch
• add a deterministic browser regression for the late-timer sequence

Upstream

Fork-adapted port of Kpa-clawbot/CoreScope#1945, applied to fork master 1d2e0fee7cc9528d6bd83ae2c95d04272d0b0335. The product fix matches upstream; the regression was added without replacing the fork's existing E2E behavior.

Verification

• red/green proof: the new step failed before the fix (moved #eab308, settled #ef4444)
• node test-channel-color-picker.js — 17/17
• local test-channel-color-picker-e2e.js — 10/10, repeated twice by the implementation pass
• independent parent browser run — 10/10
• node --check for both changed JavaScript files
• packet-filter tests — 92/92
• aging tests — 19/19
• git diff --check

Known baseline findings

Two broader, non-gating exploratory suites retain unrelated pre-existing failures: test-channel-colors.js has 19 passes/2 stale getRowStyle expectations, and test-frontend-helpers.js has 705 passes/2 stale favStar expectations. This PR does not alter those paths or relax those assertions.

Scope

No new colors, configuration values, customizer settings, dependencies, workflow changes or deployment behavior.