fix(cli): allow slashes in MIME type parameters

[Alex0AI]

Summary

The CLI currently counts every slash in --mime-type, including slashes in parameters. A valid hint such as application/json; profile="https://example.org/a/b" exits with Invalid MIME type before conversion. Conversely, a missing type/subtype separator can be masked by a slash in a parameter (text; profile=a/b).

Check the existing separator requirement only on the media type before the first semicolon. Preserve the entire original hint in StreamInfo so converters/plugins still receive its parameters. This keeps the fix scoped to the CLI's existing validation rather than introducing a new MIME parser.

Tests

• Added five regression cases: quoted URI parameters, multiple parameters, ordinary charset parameters, an extra separator in the media type, and a separator present only in a parameter.
• Before the fix: 3 failed, 2 passed.
• After the fix: 15 related CLI tests passed (10 Azure conversion cases excluded because their optional SDK dependencies are not installed).
• Actual JSON-file conversion with the quoted profile URI succeeds.
• git diff --check passed.

Investigated and implemented with OpenAI Codex assistance.

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[PRABHU KIRAN VANDRANKI (VANDRANKI)]

Community review (not a maintainer, does not clear the merge gate). I read the full diff (the one-line change in __main__.py and the new tests in tests/test_cli_misc.py), then read how mime_type_hint flows into StreamInfo and _markitdown.py. I ran it on Windows with Python 3.13.

What I ran:

• tests/test_cli_misc.py on this PR head: 25 passed. With only __main__.py put back to origin/main, 3 fail: the two test_mime_type_parameters_are_preserved cases that contain a slash inside a parameter, and test_invalid_media_type_is_not_hidden_by_parameters[text; profile=a/b]. The other new parameters pass on main too (as expected, since they already had the right slash count).
• The real CLI with stdin input (python -m markitdown --mime-type ...), not the mocked path: text/html, text/html; charset=utf-8, text/html; profile="https://example.org/p" and upper-case TEXT/HTML; profile="https://e/p" all produced the same # Hi heading. text/csv; profile=... produced the table and application/json; profile=... passed the JSON through. On main the profile form exits with "Invalid MIME type: text/html; profile="https://example.org/p\"". text; profile=a/b is still rejected on the PR, because the check now looks only at the part before the first ;.

The reasoning holds: the number of slashes in the type itself is what matters, and the old count("/") != 1 over the whole string rejected valid parameter values such as a quoted profile URI.

Notes, none blocking:

1. The full string, parameters included, is still stored in StreamInfo.mimetype (as it already was for parameter hints without a slash, like text/html; charset=utf-8). I read _markitdown.py lines 745 to 790: the extension guess via mimetypes.guess_all_extensions(base_guess.mimetype) will find nothing for a hint with parameters, and the comparison with the Magika result is an exact string compare. In my CLI runs the converters still matched, because they compare by prefix, but I only tried HTML, CSV and JSON, not binary formats such as PDF or DOCX. Splitting the parameters off into charset and the bare type, as the Content-Type header handling does around line 538 to 544, would make this uniform, but that is a separate change.
2. The check is a plain split on the first ;, so a hint such as text/plain;a="b;c/d" is accepted (I ran it, output x). That is fine, since the type before the first ; is still validated.

Looks correct and small.