feat(playground): polish first run and add real nodemon restarts

[vanilla-wave]

Summary

• make Project files a real editable multi-file starter, remove Share and project search, update the terminal hint, and keep Vite 8 experimental
• create a durable honest empty scratch when the chooser closes while hiding it from the Projects list
• run Express, Hono, and Koa through pinned nodemon 3.1.14 with real remote-FS Worker children, restart, stdio, IPC, preview, crash, recovery, and teardown behavior
• align visible runtime copy with the Node 24 parity target and update the curious first-15-min journey
• close the completed restart and generic Worker-spawn backlog items; record ADR-0202 and ADR-0211

Fidelity and architecture

• public child-process IPC uses Node-default JSON shaping; invalid sends do not poison the channel
• Worker child stdio exposes pipes versus inherited or redirected descriptors with Node-compatible nullability
• virtual ps supports a truthful default terminal selection and live PPID/PID table; unsupported formats fail loudly
• hidden-empty persistence, scratch dirty provenance, and project lifecycle are covered at owner and browser boundaries

Fault matrix

Risk	Coverage
empty scratch is shown as a project or wipes durable bytes	project-index unit/fault tests, browser owner persistence, M0 boot and lifecycle E2E
nodemon misses edits, double-spawns, or leaves a port alive	Express restart/crash/recovery/Ctrl-C E2E plus Hono and Koa E2E
nested Worker reads an empty filesystem	remote-FS browser-unit test and loud no-relay regression
IPC serialization failure disconnects later messages	Node parity and process/fork IPC regressions
stdio forwarding disagrees with public ChildProcess shape	Node parity, stdio-plan tests, and real Chromium Worker probe
parity cases leak stdin EOF or decoder state	sequential parity-runner stdin lifecycle regression

Verification

• pnpm pr:check — 12/12 passed; full Node parity 220 cases
• Chromium browser-unit remote-FS child process — passed
• Express fullstack nodemon E2E — passed
• Hono and Koa nodemon E2E — 2/2 passed
• project-management and project-switch Chromium-heavy E2E — 7/7 passed
• curious first 15 minutes — 2/2 passed
• final Standards review — zero blockers

[github-actions]

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