Release v2.15.1

fix: surface parser errors on CompassDocument in sync client (#222)

## Summary
- Sync `CompassParserClient` previously logged parser errors and
**skipped** returning those docs, so callers (e.g. North sync
`process_file` → `put_documents`) got an empty list and raised a generic
`CompassNoContentParsedError` with no details.
- Align with [async
parser](https://github.com/cohere-ai/cohere-compass-sdk/blob/f8c46703465fc888c95c00c55337df75d125a3f6/cohere_compass/clients/parser_async.py#L372),
which already adapts and returns `CompassDocument`s that carry `errors`.
- Safe for current North callers: [North already filters out docs with
`errors`](https://github.com/cohere-ai/north/blob/main/src/backend/services/compass.py#L495-L504)
before inserting, so returning errored docs does not change what lands
in their list today — it only makes the error message available for them
to surface.
- Related to
[CMPS-941](https://linear.app/cohereai/issue/CMPS-941/show-a-useful-error-for-password-protected-files-in-compass)
(one of several PRs; does not fully address the issue).
- Context: [Password protected file parsing error handling
investigation](https://app.notion.com/p/cohereai/Password-protected-file-parsing-error-handling-investigation-3a34398375db80478db6e061457df437)

## Test plan

(I pointed a local North to local compass SDK and made sure this work
with it)

- [x] Process a password-protected PDF via sync `process_file` /
`process_file_bytes` and confirm the returned `CompassDocument` includes
the parsing error (not an empty list).
- [x] Confirm successful parses still return docs unchanged.
- [x] Smoke-check North sync upload path can read `doc.errors` instead
of treating the result as “no content.”

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Co-authored-by: Cursor <cursoragent@cursor.com>