The session list opens instantly on large profiles, plus quality-of-life fixes.

Speed
- The session list now appears in a fraction of a second even with thousands of sessions (it could sit blank for several seconds before). Search is ready almost immediately.
- The first time you open the list after this update, TS-G may show "Optimizing your sessions…" for a few seconds while it prepares. This happens once.

Improvements
- Add several tags at once: separate them with commas, e.g. "work, research, reading". Undo removes them all in one step.
- The undo/redo buttons show how many steps are available as a small badge, and in their tooltip.
- Changing the date format or the open-button setting updates an open session list straight away.

Fixes
- Backups: if a session's backup file couldn't be saved, it was silently skipped from then on. It's now retried on the next backup.

Faster, and fixes for backups and restore.

Speed
- The popup opens dramatically faster on large profiles: the session list and search now read a small index instead of decoding every saved session (every tab and favicon) each time.
- Auto-save does much less work in the background after every tab change.
- Large sessions scroll smoothly in the detail pane.

Fixes
- Backups: with backups on, the "all sessions" mode wrote a full, uncompressed copy of every session every 30 minutes. It's back to once per browser session, and the compressed Complete backup is skipped when
nothing has changed.
- Opening a session in a new window did nothing when the Firefox homepage was saved without "https://". New windows now open on a blank page first.
- Backups still going to the old "TabSessionManager - Backup" folder now use "Tab_Session_Garrison_Backup" (only if you never changed it). Existing backup files stay where they are.

Polish
- The undo/redo arrows match the other header icons.
- The placeholder page for not-yet-loaded tabs uses the green theme.

Note: this update upgrades the internal session database. Your sessions are kept; going back to 0.3.0 afterwards isn't supported.