feat: add configurable terminal window title

[rabin-io]

Add a new gui.terminalTitle config option that sets the terminal
window title when opening a repository. The default format is
lazygit::{{repoName}} (e.g., lazygit::myproject).

Features:

• Configurable title format with {{repoName}} placeholder
• Set to empty string to disable terminal title updates
• Hot-reloadable: title updates when config file changes
• Cross-platform support using tcell's SetTitle()
• Windows legacy console fallback using cmd.exe's title command

Example config:

gui:
  terminalTitle: "lazygit::{{repoName}}"
  # or custom formats:
  # terminalTitle: "[{{repoName}}] lazygit"
  # terminalTitle: ""  # disable

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
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🟢 Metrics 0 complexity · 0 duplication

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[rabin-io]

Hi @stefanhaller

With the recent update to the AI contribution policy, would you prefer I close this PR? For what it's worth, I've been using this patch daily in my own Lazygit workflow, and it’s been very stable, but I understand if it can't be merged under the new rules.