fix(core): align command reload pipeline and repair plugin fixture - #39171

What

Two repairs in the config-reload area:

1. Aligns the command reload pipeline (feat(core): reload commands from config change feed #39160) with the refinements that landed in the agent plugin (feat(core): reload agents from config change feed #39167), so both config.changes consumers share one shape.
2. Fixes the long-red PluginSupervisor config > reloads an auto-discovered plugin when its file changes test: the consolidation refactor (8db7487) moved @opencode-ai/plugin's entrypoint from src/index.ts to src/promise/index.ts, and this test generates its plugin in a tmpdir where the bare package specifier cannot resolve — the absolute file URL it builds pointed at the deleted path, so the plugin never loaded. One-line path fix; the reload mechanism itself was never broken.

How

• ConfigCommandPlugin: one merged trigger stream (Stream.merge(sourceChanges, configUpdates) → one debounce → one runForEach) replaces the two separate forks, eliminating duplicate load() scans on correlated bursts and the stale-scan overwrite window on loaded.documents.
• isCommandSource uses FSUtil.contains (Windows-robust, same helper Config's reconcile uses) driven by a sourceDirectories constant.
• command.test.ts drops its inline settle/advance/drain copies in favor of test/lib/clock.ts from feat(core): reload agents from config change feed #39167, and renames the Config.Test binding to configTest to stop shadowing the bun:test import.
• plugin.test.ts: mutablePlugin imports ../../../plugin/src/promise/index.ts.

Testing

• Command + agent matrices: 21/21, stable across 5 consecutive runs.
• test/config/plugin.test.ts: 11/11 (previously 10/11), stable across 3 consecutive runs — this removes the last inherited test/config failure from base CI.
• bun typecheck clean.