fix: replace bare excepts in tg-set-prompt, structured-data cleanup and API docs generator

[Thorsrud22]

Refs #783. Takes the slice I claimed on the issue: three of the remaining bare except: clauses outside tests/ on release/v2.9.

Summary

• trustgraph-cli/trustgraph/cli/set_prompt.py:129: the --schema parse catches json.JSONDecodeError only, and chains it (raise ... from e) so the position of the JSON error is kept on the RuntimeError.
• trustgraph-cli/trustgraph/cli/load_structured_data.py:167: the temp-descriptor cleanup in the finally block catches OSError only (which covers FileNotFoundError).
• docs/generate-api-docs.py:112: the inspect.signature fallback catches TypeError and ValueError, the two exceptions it documents raising, instead of everything.

Behaviour for the normal paths is unchanged; only KeyboardInterrupt/SystemExit (and unrelated bugs) now propagate instead of being silently swallowed.

Tests

• New tests/unit/test_cli/test_set_prompt_errors.py: invalid --schema JSON produces the existing "JSON schema must be valid JSON" message and never calls the API; a valid schema is passed through parsed; a KeyboardInterrupt raised inside the parse propagates.
• PYTHONPATH=trustgraph-cli:trustgraph-base python -m pytest tests/unit/test_cli/test_set_prompt_errors.py tests/unit/test_cli/test_load_structured_data.py: 10 passed, 2 skipped (pre-existing skips).
• python -m py_compile on the three edited files.

Not touched: load_doc_embeds.py / save_doc_embeds.py (claimed by @chiruu12) and the two ontology files, which are still open for someone else.

[github-actions]

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[cybermaggedon]

@Thorsrud22 are you able to action the CLA?

[Thorsrud22]

Thanks for asking, @cybermaggedon. I'd rather not sign a CLA, so I'm closing this. The changes are small and self-contained, so anyone is welcome to pick them up. Sorry for not noticing the CLA requirement before opening it.