Release awwan v0.13.1 (2026-02-09)

**🌼 internal/cmd/www-awwan: implement socket based activation using systemd**

This allow us to run www-awwan only when its activated in the local
environment.

**🌼 cmd/awwan: implement socket based activation on serve command**

The "awwan serve" command now can run based on socket activation under
systemd.

**🌼 _wui/doc: use default ciigo style**

The default ciigo style provides consistent style with kilabit.info
and have support for light and dark themes.

**💧 all: fix data race in tests and [httpServer.ExecuteTail]**

In the test for AwwanLocal, use buffer with lock, so each write and
read is safe.

In the httpServer, the test found data race during ExecuteTail when
accessing [ExecResponse.EndAt].
We fix it by locking the resource during call to end() and when
accessing the EndAt field.

**💧 _ops/awwan-tour: fix build with latest mkosi**

The option "Incremental" and "CacheDirectory" in mkosi.conf has been moved
to section "[Build]".

**💧 all: use separate buffer for stdout and stderr in TestAwwanLocal**

This is to fix flaky test on TestAwwanLocal.

**🌼 all: improve the Server-Sent Events (SSE) output**

In the ExecResponse, store the event in the Output instead of message
data, so the server can iterate the Output directly and pass it to
WriteEvent directly.

The event ID now start at 1 with type "begin".
This is to minimize confusion when comparing empty Last-Event-ID from
client, which is equal to 0.
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