Find libmosquitto and ship it in release packages (iteration 2, step 1)

cmake/Mosquitto.cmake finds it through pkg-config; with
FRAMEASSISTANT_SHIP_MOSQUITTO=ON (all package presets) it installs
lib/libmosquitto.so.1 and Debian's copyright file and excludes the
library from the Qt bundler (D35). The build containers get
libmosquitto-dev, the test container the mosquitto broker.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -153,6 +153,9 @@ sequenceDiagram
   - `libopenvr_api.so` next to the executable
   - install rules and registration for Qt bundling
   - the check against SteamVR process names
+- **`cmake/Mosquitto.cmake`** (app, not platform) finds libmosquitto through pkg-config. With
+  `FRAMEASSISTANT_SHIP_MOSQUITTO=ON` (all package presets) it installs the library into `lib/`
+  under its soname plus Debian's copyright file, and excludes it from the Qt bundler.
 - **App identity** (root `CMakeLists.txt`): `project()` name and version, `VRDASH_APP_KEY`,
   `VRDASH_DISPLAY_NAME`, `VRDASH_EXECUTABLE_NAME`, texture size. CMake generates from them
   `AppConfig.h` and the SteamVR manifest, with `binary_path_linux_arm` for ARM builds and

docs/PROGRESS.md

@@ -22,8 +22,9 @@ CLAUDE.md ("Working rules").
 
   The error itself is covered off the device by `tst_config`. Checks 3 and 4 run in the next
   session on the Frame (iteration 2 testing needs it too).
-- **Implementation** follows the order in DESIGN.md (steps 1–7); step 1: libmosquitto in
-  CMake and the containers.
+- **Implementation** follows the order in DESIGN.md (steps 1–7). Step 1 (libmosquitto in
+  CMake and the containers) done; next: step 2 (`MqttClient`, `MosquittoClient`,
+  integration test).
 
 ## Next steps
 
@@ -124,6 +125,14 @@ Known limitation: the bundled-Qt package does not support WebEngine in this iter
 - Design of iteration 2 written (DESIGN.md). User's decisions: libmosquitto's own thread
   (D42), app commands in the platform for `--ha-remove` (D43), committed TLS test
   certificates (D44). Design approved; phase 3 started.
+- Step 1: `cmake/Mosquitto.cmake` (pkg-config; `FRAMEASSISTANT_SHIP_MOSQUITTO=ON` in all
+  package presets installs `lib/libmosquitto.so.1` and Debian's copyright file, which already
+  contains the EPL-2.0/EDL-1.0 texts); `libmosquitto-dev(:arm64)` in the build containers,
+  `mosquitto` in the test container; THIRD_PARTY_NOTICES entry. Checked: host configure finds
+  2.1.2; `container-test.sh` 8/8, no Vulkan validation messages; the cross build stages
+  2.0.21 (aarch64) and the copyright file. The binary doesn't need the library yet (nothing
+  calls it; `--as-needed`), which changes in step 2. On the host, the GUI tests can't run in
+  this session (no display).
 
 ### 2026-10-05: requirements approved