Feat: add regex-based title cleaning rules configuration and implementation

[AminZibayi]

You can configure regex-based title cleaning rules to modify window titles before they are sent to the server. This is useful for removing application-specific suffixes, temporary states (like unread message counts), or other noisy data from window titles, leading to cleaner and more accurate data aggregation.

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[!IMPORTANT] Add regex-based title cleaning rules to modify window titles before sending to server, with configuration and documentation updates.

• Feature:
  • Add regex-based title cleaning rules to modify window titles before sending to server.
  • Implemented in clean_window_title() in main.py and get_title_cleaning_rules() in config.py.
  • Configuration examples added to example-config.toml.
• Configuration:
  • Users can define rules in ~/.config/activitywatch/aw-watcher-window.toml.
  • Each rule includes app, pattern, and replacement fields.
• Documentation:
  • Updated README.md with instructions for configuring title cleaning rules.

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