docs(config): document file data source upload limits

[s5unanow]

Summary

Documents the configurable File data source upload limits introduced by EPMCDME-13212 on the CodeMie API Configuration Reference page (/admin/configuration/codemie/api-configuration/). The page previously did not mention the 10-file cap on File data sources at all; the backend now exposes it, together with two related settings, as environment variables.

Changes

• Added FILE_DATASOURCE_MAX_UPLOAD_COUNT, FILE_DATASOURCE_MAX_UPLOAD_TOTAL_SIZE and FILE_DATASOURCE_UPLOAD_MAX_WORKERS to the General Storage Settings table (defaults, constraints, and when to raise them)
• Added a "File data source upload limits" info block explaining where the limits are enforced (POST/PUT /v1/index/knowledge_base/file, HTTP 422), the concurrent upload workers, and that the configured count is advertised as fileDatasourceMaxUploadCount in GET /v1/info and picked up by the UI automatically

Testing

• Tested locally with npm run build (full production build; npm start was not used)
• All pages render correctly (verified in the built output)
• Images display properly (no images in this PR)
• Internal links work (no new links; build runs with onBrokenLinks: 'throw')
• Sidebar navigation works (no sidebar changes)

Quality Checks

• npm run check passes (typecheck + lint + commitlint)
• No MDX compilation errors
• No raw angle brackets (<text> must be `<text>`)
• Sidebar references document IDs (not filenames)
• Images stored locally next to content (not in static/img/)
• Commit messages follow Conventional Commits
• No secrets or credentials in documentation

Additional Notes

• Content is derived from the merged implementations of EPMCDME-13212: backend codemie MR !3939 (settings, validators, /v1/info field) and UI codemie-ui MR !1645 (the UI consumes the advertised limit and falls back to 10).
• Defaults and constraints were verified against src/codemie/configs/config.py on main. The MR description mentions only the file-count setting, but the merged commit also added the combined-size cap and the worker count, so all three are documented together.
• The user-guide page "Add and Index File DataSource" still lists only per-file size limits and does not mention the file-count limit; that is a separate gap left for a follow-up.

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https://claude.ai/code/session_01AxXUhubD1gC1UaeABscyQw