flatpak: run host interpreters via flatpak-spawn; validation --mode flag

py_func, lua_func and the run item now reach host binaries through
`flatpak-spawn --host` instead of trying to load them under the
sandbox runtime (which fails with a glibc ABI mismatch). Adds
`--talk-name=org.freedesktop.Flatpak` to the manifest, stages the
/app/lib/testium tree under /tmp so the host can read it, and drops
the dead `_FLATPAK_HOST_DIRS` / lib-injection code paths that the
new approach makes obsolete.

Validation suite gains a `--mode source|wheel|pyinstaller|flatpak|
appimage` flag so the same item set can run against every packaging
channel; per-mode report file names avoid clobbering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

release_note.txt

@@ -16,6 +16,14 @@ version 0.1.3
   path, default report/log dirs, python/lua interpreter pickers) now
   bypasses the XDG document portal — the v0.1.2 fix was only on the
   "open test" dialog.
+- Flatpak: py_func / lua_func / run sub-instance now execute on the host
+  via flatpak-spawn, lifting the previous glibc/ABI incompatibility that
+  prevented user-configured host Python or Lua interpreters from being
+  reached from the sandbox.
+- Validation suite: single entry point with ``--mode source|wheel|
+  pyinstaller|flatpak|appimage`` to validate any packaging channel
+  against the same item set; reports are stamped per mode.
+- GUI: the "Run tum" test item now uses the testium logo.
 
 version 0.1.2
 ==============