US09-03: Write the Architecture Overview (#109)

docs/index.md

@@ -15,6 +15,9 @@ repository under `docs/`, on Gitea, and inside the running application under
 2. [Installation and operations](installation.md) — host and container installation,
    every setting, the first-run checklist, upgrades, backup and restore, and what
    each refusal at startup means.
+3. [Architecture](architecture.md) — the context and runtime diagrams, what each
+   module owns, the three journals a restart reads, and where every invariant is
+   enforced.
 
 ## Being written
 
@@ -22,8 +25,6 @@ The remaining manuals are accepted work, not aspiration; each is a story in
 [E09](https://git.domverse-berlin.eu/domverse/photoanalyzer/src/branch/main/delivery_backlog/E09-documentation.md)
 and will appear here as it lands.
 
-- **Architecture** — context and runtime diagrams, the module map, the job and
-  journal state machines, and where each invariant is enforced (US09-03).
 - **User manual** — one page per workflow stage with screenshots of the real
   application, and a catalogue of every error and refusal (US09-04).