docs: public-ready README, thumbnail, and accurate license

[basilebong]

Summary

The repo is now public under the Hightecc org, but the README still read like a private internal doc. This makes it public-ready: it stops pointing at the private production domain, tells the truth about what is actually built, fixes the license description, and presents the project with a screenshot and a short feature list.

What changed and why

• Dropped every reference to the private production domain (app.hejmly.com) in favor of a <your-domain> placeholder, so the public README does not hardcode the live deployment.
• Documented the recipes app, which already exists but was undocumented (intro, layout tree, and MCP tool list).
• Corrected MCP tool names from dotted (grocery.list_items) to the real double-underscore names (grocery__list_items, recipes__list, and so on), which is what the code registers.
• Rewrote the Elastic License 2.0 description to be accurate: free to self-host, use, modify, and redistribute; offering it to others as a hosted or managed service needs a separate commercial license.
• Removed the stale "pre-v0 / scaffold only" warning (it runs end to end) and set the badge to v0.0.1.
• Removed a dangling "See the full architecture spec" link (no such doc) and the "It is not a hosted service" line.
• Removed all em dashes.
• Added a centered app screenshot (docs/thumbnail.png) and a short feature list under the title.

How to verify

• Open the README on this branch in GitHub: the thumbnail renders, the feature list reads cleanly, and there are no remaining app.hejmly.com references.
• Searching the README for em dashes and for hejmly.com both return nothing.

Not in this PR

• .env.example still has 4 app.hejmly.com references; the Caddyfile keeps the domain only as a parameterized default. Both can be a follow-up if wanted.