feat: add --no-view-file flag for interactive viewer (#428)

[ShivamB25]

Summary

• add a new --no-view-file flag and no-view-file config option to disable file content viewing in interactive mode
• block file viewing via both keyboard (v) and mouse double-click, with user feedback and help text updates
• add tests for app wiring and TUI behavior, and update README/configuration/man docs

Testing

• golangci-lint run
• go test ./cmd/gdu/app ./tui
• go test ./...

Closes #428

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.33%. Comparing base (ede21d2) to head (79d1589).

Additional details and impacted files

@@ Coverage Diff @@ ## master #496 +/- ## ========================================== + Coverage 81.42% 83.33% +1.91%  ========================================== Files 49 49 Lines 5126 5156 +30 ========================================== + Hits 4174 4297 +123  + Misses 816 721 -95  - Partials 136 138 +2 

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[dundee]

Nice, thanks!