A run page shows its log live from /events and opens no EventSource of its own #2843

Split from #2835 (parked twice). Both pulls before this failed one test: test/map.test.ts › "the drawing is a live region scoped to its repository, fits, and pans". That test asserts the literal new EventSource('/events') in every page's script, because src/web/client.ts is shipped on every page. Keep that line in connect() as it is. Run bun test test/map.test.ts before you push.

Done looks like:

• [ ] The run page's log tail (the new EventSource(url) near src/web/client.ts:364, rendered by src/web/studio/run.ts) appends lines from the run.log frames for its run, received over the one /events connection (the forge event the shared stream already dispatches). The per-run stream URL is no longer opened from this page.
• [ ] On first paint the log is still server-rendered from the file. Lines that arrive before the paint are not shown twice.
• [ ] Test: a run page's HTML and script open no EventSource except /events, and test/map.test.ts passes unchanged.

Files: src/web/client.ts, src/web/studio/run.ts, a test under test/.

Parked by the crew: the check failed ("apps, runs and the crew on the web > the runs list, one run's log page, and the short door to it") and the decider saw no point in another try (pull #2851 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.