fix(my_egeria): serve_my_* page URLs follow the browser's address

[dwolfson]

Summary

Makes serve_my_profile / serve_my_egeria work from any hostname, so one container serves localhost, the machine's name and a demo site alike.

The problem: textual-serve builds every asset and WebSocket URL in the page from one fixed public_url. The egeria-workspaces portal is configured for https://laz.local:8843/my-egeria. A browser that reached it as https://localhost:8843 was sent to another origin; the page's CSP blocked the script, and My Profile showed only its title.

The fix: a textual_serve.Server subclass whose handle_index computes the base URL per request.

• Behind a proxy (X-Forwarded-Host or X-Forwarded-For):
  • host: the first valid X-Forwarded-Host entry, else Host;
  • scheme: X-Forwarded-Proto, else the configured public URL's scheme;
  • path: the configured public URL's path (/my-egeria).
• Direct connection: the request's own scheme and host. Previously textual-serve pointed browsers at 0.0.0.0.
• Why skip invalid entries: egeria-workspaces' Apache actually sends X-Forwarded-Host: i=99, localhost:8843, from a misconfigured RequestHeader line. That's been reported to that repo.
• Concurrency: Server.handle_index builds its URLs synchronously, so swapping public_url for the duration of one request can't interleave with another.

Docs: the handoff doc, integration doc and My Profile manual now explain that only the path and scheme come from MY_EGERIA_PUBLIC_URL.

Testing

• New tests/micro-tests/test_my_egeria_serve.py: serves real textual-serve pages through aiohttp's test server and fetches them as localhost, laz.local, a demo hostname, IPv6, direct connections, and the exact junk header Apache sends. Plain textual-serve fails the localhost case. The full tests/micro-tests suite passes.
• Live, in the portal's quickstart-my-profile container (with this serve.py): both https://localhost:8843 and https://laz.local:8843 get same-origin URLs, load textual.js, and render My Profile's welcome screen over the WebSocket, with no errors.

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