Fix broken internal links in concept files

[ChristopherA]

Description

Several concept files have broken internal links that need to be fixed:

Files with broken links:

1. concepts/progressive-trust.md (line 457)

   • Current: [XID Fundamentals](xid-fundamentals.md)
   • Should be: [XID Fundamentals](xid.md)

2. concepts/public-participation-profile-examples.md (lines 17, 409)

   • Line 17: progressive-trust-lifecycle.md → should be progressive-trust.md
   • Line 409: progressive-trust-lifecycle.md → should be progressive-trust.md
   • Line 409: xid-fundamentals.md → should be xid.md

Note

The public-participation-profile-examples.md file also has a warning at the top indicating it hasn't been fully checked and proofed, so it may need additional review beyond just fixing the broken links.

Related PRs

This follows up on the documentation improvements made in:

• PR docs: improve concepts/README.md as entry point and update descriptions #9: Improved concepts/README.md
• PR docs: sync main README with improved concepts/README #10: Synced main README.md with concepts improvements
• PR docs: fix broken concept links in LEARNING_PATH.md #11: Fixed broken links in LEARNING_PATH.md