Align CI with the validated Ubuntu support floor

Stop implying that one Ubuntu 3.11 unit lane validates the full Linux support surface Aman documents.\n\nSplit CI into an Ubuntu CPython 3.10/3.11/3.12 unit-package matrix, a portable install plus doctor smoke lane, and a packaging lane gated on both. Add a reproducible ci_portable_smoke.sh helper with fake systemctl coverage, and force the installer onto /usr/bin/python3 so the smoke path uses the distro-provided GI and X11 Python packages it is meant to validate.\n\nUpdate the README, release/distribution docs, and Debian metadata to distinguish the automated Ubuntu CI floor from broader manual GA signoff families, and add the missing AppIndicator introspection package to the Ubuntu/Debian dependency lists.\n\nValidate with python3 -m unittest discover -s tests -p 'test_*.py', python3 -m py_compile src/*.py tests/*.py, and bash -n scripts/ci_portable_smoke.sh. The full xvfb-backed smoke could not be run locally in this sandbox because xvfb-run is unavailable.

docs/releases/1.0.0.md

@@ -15,7 +15,10 @@ This is the first GA-targeted X11 release for Aman.
 - `systemd --user` for supported daily use
 - System CPython `3.10`, `3.11`, or `3.12` for the portable installer
 - Runtime dependencies installed from the distro package manager
-- Representative validation families: Debian/Ubuntu, Arch, Fedora, openSUSE
+- Automated validation floor: Ubuntu CI on CPython `3.10`, `3.11`, and `3.12`
+  for unit/package coverage, plus portable install and `aman doctor` smoke
+  with Ubuntu system `python3`
+- Manual GA signoff families: Debian/Ubuntu, Arch, Fedora, openSUSE
 
 ## Artifacts