Rename the workspace layout: fluksio -> app, website -> index

The repo moves to git.stroblme.de:Fluksio/app.git and its sibling to
Fluksio/index.git, so every cross-repo path reference moves with it. The
architecture sources the roadmap cites now live in the docs repo under
architecture/, and the brand marks in the index repo's src/assets.

Also replaces the placeholder README with one that reflects the actual layout.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

NOTEPAD.md

@@ -15,7 +15,7 @@ Deferring because out of scope is fine, but don't mention deferring than.
 - CHORE/FLOW: the flow test files live in `backend/app/flow/test*.py`, inside the package
   rather than `backend/tests/`, so `coverage run -m pytest tests/` never collects them.
 - CHORE/INFRA: port the n3xd CI workflows (pre-commit, backend tests, Playwright shards,
-  compose smoke) to `.forgejo/workflows/`. Codeberg runs Forgejo Actions and needs CI
+  compose smoke) to `.gitea/workflows/`. The Gitea instance runs Gitea Actions and needs CI
   enabled per repository.
 - FEAT/UI: `@xyflow/react` and a Monaco editor belong here once the node canvas starts.
   The website already demos `@xyflow/react` on its features page.
@@ -31,3 +31,7 @@ Deferring because out of scope is fine, but don't mention deferring than.
 
 - FEAT/INFRA: Redis, MQTT broker and InfluxDB compose services. Blocked on the flow engine
   being reachable from the API — no runtime path imports them today.
+- CHORE/INFRA: `bun install` inside the frontend Docker build intermittently fails with
+  "Fail extracting tarball" for several packages at once, and succeeds on a plain rebuild.
+  It looks like concurrent extraction under memory pressure. Pin down or retry in the
+  Dockerfile if it starts costing CI time.