feat(install): support Raspberry Pi OS Bookworm (Python 3.11) alongside Trixie (3.13) (#689)

The installer and scripts/check_system_compatibility.sh share one set of OS rules (scripts/install/lib_os.sh): Bookworm (Debian 12, Python 3.11) and Trixie (Debian 13, Python 3.13) are supported, python3 older than 3.11 stops the install before anything changes, and dhcpcd gets a warning with directions. setcap targets /usr/bin/python3, the apt fallback honours the requirement floors, and the desktop check no longer misreads under pipefail. CI runs the unit and plugin-safety suites on 3.11 and 3.13 (tooling jobs on 3.13); mypy targets 3.11.

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

mypy.ini

@@ -6,8 +6,9 @@
 files = src
 exclude = (^|/)(test|__pycache__)/
 
-# Python version
-python_version = 3.10
+# Python version: the oldest the installer supports (Raspberry Pi OS
+# Bookworm ships 3.11; Trixie ships 3.13).
+python_version = 3.11
 
 # Platform (Linux/Raspberry Pi)
 platform = linux
@@ -103,8 +104,8 @@ ignore_missing_imports = True
 
 
 # numpy's own stubs (numpy>=2.3) use Python 3.12 `type` statements, which mypy
-# refuses to parse under python_version = 3.10 -- and 3.10 is the floor this
-# code has to run on, so it stays. Treat numpy as Any instead: skip it, and
+# refuses to parse under python_version = 3.11 -- and 3.11 (Bookworm) is the
+# floor this code has to run on, so it stays. Treat numpy as Any instead: skip it, and
 # follow_imports_for_stubs makes the skip apply to its .pyi files too.
 [mypy-numpy.*]
 follow_imports = skip