Use full path for poetry command in system update to ensure binary is found

- Change poetry command to use absolute path ~/.local/bin/poetry
- Add comment explaining poetry location in user's local bin directory
- Prevents command not found errors when poetry is not in system PATH

src/auracast/server/multicast_server.py

@@ -1037,9 +1037,10 @@ async def system_update():
             log.error("git checkout failed: %s", stderr.decode())
             raise HTTPException(status_code=500, detail=f"git checkout failed: {stderr.decode()}")
 
-        # 2. Run poetry install
+        # 2. Run poetry install (use full path as poetry is in user's ~/.local/bin)
+        poetry_path = os.path.expanduser("~/.local/bin/poetry")
         proc = await asyncio.create_subprocess_exec(
-            "poetry", "install",
+            poetry_path, "install",
             cwd=project_root,
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE