[C-Hipple]

Summary

PR #303 gave the server a way to notify a client (Subscribe + Notifier.Notify), but the only thing it sent was a heartbeat. This PR has the server announce plugin and AI feature results as they change. All three clients (the web client, the Chrome extension and Emacs) now follow those announcements and no longer poll for either.

The server sends two new notifications. Each one names the PR, the plugin or feature, and its new status. Neither carries the output, which can be large. A client showing that PR reads GetPluginOutput or GetAIOutput again when it gets one.

• Server.PluginOutputChanged is sent every time a plugin result is written (pending, success, error, deferred) or cleared by RerunPlugins.
• Server.AIOutputChanged is sent when an AI run is claimed (pending) and again when its result is stored. This covers every run: ones a client asked for, the applied features, and the automatic ones.

A notification sent while a client is disconnected never arrives. So each client also reads everything again when it (re)connects or a new server subscribes.

Changes

• Server
  • All plugin result writes now go through storePluginResult, which sends the notification after the upsert. RerunPlugins announces each result it clears before it replies.
  • The ai package can't import server, so ai.Runner gets an OnChange hook. RunServer points it at the notifier.
  • store now returns the status it actually stored.
• Web client
  • A new shared useServerChanges hook replaces the poll loops in usePluginOutputs, useAIReport and useAIBackgroundRuns. It re-reads when a change names the PR, and on SSE reconnect via a new ServerEvents.onOpen. Reads run one at a time, and a burst of changes becomes one extra read.
  • useAIReport only applies a reply newer than the one it's showing, so a stale RunAIFeature reply can't overwrite the landed result.
  • The "still running, check back later" notice and the poll timing constants are removed.
• Chrome extension
  • The native protocol now recognises notifications, whole or chunked. NativeClient subscribes each new server before sending it anything else, asking for the slowest heartbeat.
  • The service worker relays the two events to extension pages over a crs-events port and refuses that port to anything else, the same rule as for RPC. When a new server subscribes, it tells pages to resync.
  • PRTools re-reads on these events. The 3 s poll, the 10 s "just requested" grace period and poll_utils are gone.
  • The content script no longer re-asks for the file order every 5 s. The service worker tells a PR's tabs when a file-ordering result lands.
• Emacs
  • crs-start-server subscribes, and the process filter dispatches notifications to crs-server-notification-functions.
  • Open plugin, AI report and change-diagram buffers for the PR refresh themselves and keep point.
  • A plugin run started from Emacs is announced in the echo area when it lands. The docstrings no longer tell you to refresh by hand.
  • The AI poll timer is removed, along with crs-ai-poll-interval and crs-ai-poll-timeout.
  • Fixed along the way: the plugin refresh used to render into whichever buffer was current when the reply arrived.
• Docs: protocol.md documents both notifications. The client docs, the extension README and CLAUDE.md are updated.

Note: the clients expect a server that sends these notifications. Against an older crs, plugin and AI views show what they read when opened, and you refresh them by hand.

Test Plan

• go build ./... passes
• go test ./... passes. New tests check that every plugin write and AI claim/landing is announced, that each announcement matches what a read would see at that moment, and that a skipped or up-to-date run announces nothing.
• bun_client: lint, format, type-check and unit tests pass, and the e2e suite passes (86 passed, plus the one known test.fail() bug). The e2e fake now runs reruns and AI runs on timers and announces each step, instead of finishing them after a set number of reads. New specs check that nothing is read while a held run is pending, and that runs the page didn't start still show up.
• chrome_extension: lint, format, type-check, unit tests and build pass. New unit tests cover notification classification, subscribing per server, the relay, port refusal, resync and the file-order nudge. All the e2e specs, new and existing, passed here. New specs cover a server-started run, no reads while one is pending, and a newly landed file order applied to an open Files changed tab. One caveat: this container's Chromium doesn't match the pinned Playwright version, so each full run had about one random spec fail in the service-worker startup fixture (chrome is not defined). The base commit fails the same way here, so it's environmental, but CI's run is the real check.
• Emacs: 68/68 ERT tests pass. Byte-compiling adds no new warnings in the changed files.

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