chore: keep generate_sites.py manual; validate in the generator instead

The database changes rarely, so regenerating by hand after editing it is
the right cost, and propagating to all 16 repos from CI would need a
token with write access to every one of them.

Drops the ecosystem-map workflow added moments ago and moves its
repos_db.json validation into generate_sites.py, which runs it before
touching anything and exits non-zero on a bad entry. That puts the check
at the moment someone would actually notice it -- the manual run -- and
removes a CI job that would have failed on any DB edit pushed before the
generator was run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: bdbarnett

README.md

@@ -39,8 +39,10 @@ running it twice produces no second diff. Repos it cannot find are skipped with
 `[SKIP]` line. It also writes the markdown ecosystem map into
 `dotgithub/profile/README.md` and `pydevices/docs/ecosystem.md`.
 
-A [workflow in `.github`](https://github.com/PyDevices/.github/blob/main/.github/workflows/ecosystem-map.yml)
-validates the database and fails if `profile/README.md` has drifted from it.
+Regeneration is **deliberately manual** — the database changes rarely, and
+running the generator is a one-line step when it does. It validates the database
+on every run and exits non-zero on a malformed entry, so the check happens at the
+moment you would notice it.
 
 ## Deployment