Keep uploaded originals beside Knowledge Store source cards - #668

What changed

• Store new uploads beside their cards in sources/, with Git attributes that preserve original bytes.
• Use versioned links where available for web pages and existing corporate files. Keep legacy cards, citation redirects, and original references readable.
• Verify uploaded originals are present, match the card's SHA-256, and can be committed. Read a Markdown original as evidence rather than as another OKF card.

How it is verified

• Local documentation, Knowledge Store compatibility, and targeted intake-profile checks pass.
• A temporary Git repository with line-ending conversion enabled preserves the exact staged bytes of Markdown and extensionless originals under the documented attributes.

Checklist

• Based on main and limited to one concern.
• Commit signed off for DCO.
• No internal work-item references.