fix: support Ubuntu 26.04 install and Qt timers

[TimInTech]

What changed

• bind HistoryPanel and HistoryEntryWidget reset timers to their Qt owners instead of using context-free QTimer.singleShot callbacks
• add a regression test that destroys the owning C++ widgets before short real timer deadlines elapse
• correct installer/autostart guidance and document the verified Ubuntu 26.04 GNOME/Wayland native-install path
• clarify that the AI-workflow setting stores only an API-key environment variable name; the secret itself belongs only in ~/.config/blitztext-linux/secrets.env
• run the complete CI workflow on Python 3.11, 3.12, and 3.14

Why

PyQt 6.11 with Python 3.14 exposed a lifetime bug: a static timer callback could run after deleteLater() had destroyed the C++ widget, aborting the Python process. Owner-bound QTimer instances are destroyed with their widgets and prevent the stale callback.

The install guidance also described systemctl --user start as enabling autostart even though the installer already enables the user service. Ubuntu 26.04 ships Python 3.14, so that verified runtime now needs equal CI coverage.

Validation

• python3 -m compileall app tests
• QT_QPA_PLATFORM=offscreen WHISPER_GUI_TESTS=1 .venv/bin/python -m pytest -q — 524 passed, 2 skipped on Python 3.14.4
• tests/test_state_machine.py — 30 passed
• focused installer/verify tests — 14 passed
• bash -n scripts/install.sh scripts/verify.sh
• git diff --check
• repository secret hygiene scan
• Ubuntu 26.04 GNOME/Wayland live verification — 18 PASS, 0 FAIL, 0 WARN, including recording, local Whisper, global hotkey, clipboard, auto-paste, tray, and autostart

Flatpak remains an experimental developer spike and is unchanged. PR #54 is handled separately after this PR.

[chatgpt-codex-connector]

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