Rename the architecture diagram to docs/architecture.*

docs/logstream-schema-logique.{png,excalidraw} become
docs/architecture.{png,excalidraw}; the README image and source link
follow.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -10,6 +10,24 @@ devices ──514 udp/tcp──▶ logstream (Go) ──HTTP batches──▶ Vi
                               └──── API / UI ◀─────────┘
 ```
 
+## Architecture
+
+![Schéma logique de Logstream](docs/architecture.png)
+
+- **Ingestion**: syslog (UDP/TCP) and Docker container logs both go through `sink()` (reverse DNS
+  on IP hosts), then the `Store` queue, which sends them in batches to VictoriaLogs.
+- **Live view**: `sink()` also publishes each message to the `Hub`, which streams it to the
+  browsers over SSE.
+- **Search**: the HTTP API turns the UI filters into LogsQL queries sent to VictoriaLogs.
+- **Timeline**: `/api/histogram` (`histogram.go`) counts the logs per interval and severity,
+  aligned on the local time; the zoom bounds (`from`/`to`) also apply to the list and the export.
+- **State**: tags and source settings live in `/data` (`logstream-data` volume); the logs
+  themselves in the `vlogs-data` volume.
+
+The editable source of the diagram is
+[`docs/architecture.excalidraw`](docs/architecture.excalidraw)
+(open it on [excalidraw.com](https://excalidraw.com)).
+
 ## Getting started
 
 ```bash