Potential fix for code scanning alert no. 2: Uncontrolled data used in path expression

[ilesinge]

Potential fix for https://github.com/ilesinge/shabda/security/code-scanning/2

Use a safe path construction and containment check before writing the file.

Best fix in this snippet:

1. Build filename using sanitized components (word, language, gender) rather than raw word.
2. Use os.path.join instead of string concatenation.
3. Normalize to an absolute canonical path (os.path.realpath).
4. Verify the resulting path stays under word_dir (also canonicalized) using os.path.commonpath.
5. Raise an error if path escapes the base dir.

In shabda/dj.py, update speak() around lines 111–148:

• add sanitization for word and gender similar to language.
• replace current filepath = ... with safe join + realpath + containment guard.
• keep existing behavior (still writes .wav in sample directory), only rejecting unsafe constructed paths.

No new imports are needed (os and re already exist).

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