Add screenshots/GIFs to README so people can visualize the app

[offendingcommit]

Problem

The README has no visuals. New visitors can't tell what OpenConcho looks like or what it does without cloning and running it.

Proposal

Capture screenshots (and ideally a short GIF/video) of:

• Dashboard with workspaces + queue status
• Workspace detail (peers, sessions)
• Session view with conclusions
• Chat view
• Settings / connection screen
• Light + dark theme side-by-side

Store under docs/screenshots/ (or .github/assets/). Embed in README under a "Screenshots" section near the top.

Notes

• Use the demo-mode masking so no real data leaks.
• Consider a high-DPI capture (2x) for sharpness.
• Could be automated via Playwright (we already have it wired up) — capture on every release.