Improve error messages in kiwix-manage

[shrrrriya]

Fixing #572

This PR improves user-facing error messages in kiwix-manage.

• Clarifies the message when a requested book ID is not found
• Adds helpful hints when adding a ZIM file fails, without changing behavior

This follows the discussion about improving error clarity without introducing
exception handling.

[kelson42]

@shrrrriya Thank you for your PR. I think it would be great if you implement the code analysing the problem and delivering the precise error message in a second commit. To me so far looks good, but I let @veloman-yunkan making the technical analysis.

[veloman-yunkan]

Please first enhance kiwix::Manager::addBookFromPathAndGetId() to signal failure by throwing an exception and add unit tests for all reasons of detectable failure (this must be done in the libkiwix repository). Then change this PR to report errors by catching exceptions emerging from that function.

[shrrrriya]

Thanks for the review and guidance.

I have now updated libkiwix to make
Manager::addBookFromPathAndGetId() throw specific exceptions
(FileNotFound, InvalidZim, LibraryNotWritable) and added unit tests
covering detectable failure cases.

PR: kiwix/libkiwix#1267

I will now update this PR to catch those exceptions and report precise
user-facing errors in kiwix-manage.

[kelson42]

I will now update this PR to catch those exceptions and report precise
user-facing errors in kiwix-manage.

Thank you, don't forget this last part.