docs: fix stale voicepoc references and dev-setup instructions

[jlocala1]

Following the README on a fresh clone currently fails in a few places. This PR makes the documented setup path actually work, verified end-to-end on a clean checkout (install → upload → playback in the browser).

The bug (commit 1): in dev mode the media player is broken for every upload. The client requests media at /artipods/{id}/{file}, but vite.config.ts only proxies /api and /uploads — so Vite's SPA fallback answers with index.html (a 200 with text/html), and the player shows "Unable to load media. The server may be unavailable." Easy to miss because the network tab shows all 200s. Fix: proxy /artipods to the API server like the other routes.

The docs (commit 2):

• cd voicepoc- → cd pulseclip in README/USAGE (leftover from the repo's original name; there is no such directory after cloning)
• Marked the server/.env step as required — without it the server defaults to port 3000 and collides with the Vite dev server
• Transcription now auto-starts after upload; documented the >100MB async flow and GET /api/transcribe/status/:jobId (from feat: async transcription for large files with polling UI #17)
• curl examples updated to artipod URLs (the documented /uploads/file.mp3 form no longer matches how /api/transcribe resolves files)
• Removed the "must be < 500MB" troubleshooting entry (limit removed in Remove 500MB multer file size limit for uploads #16); added entries for the placeholder-API-key error and why Featured Pulses 404 on a fresh local install
• Production serve section now says npm run prod — Express already serves client/dist itself
• Renamed root package voicepoc → pulseclip (package.json + lockfile)

No behavior changes outside the dev proxy; server code untouched.

[jlocala1]

Trimmed to docs-only — the /artipods Vite proxy landed on main via the #22 lineage, so that commit dropped out on rebase. What's left: voicepoc→pulseclip rename in package.json, real clone URL, current endpoint docs (artipods + async-transcription polling), the .env port-collision note, and the featured-pulses local-404 note. Independently mergeable.