[Doc] Improve IOTA Identity Docs

[lautarogiambroni]

Description

Update the IOTA Identity wiki – Introduction page to reflect the latest positioning and branding. This includes updating visuals, refining terminology, and removing outdated references.

Reference material

• [Header image link] https://drive.google.com/drive/folders/1nBmFyDunP1-R8dB56BsEM3RviqQ9a-Y-

To-do List

• Update header with the new image from the provided link
• Change title to IOTA Identity (remove the word "framework")
• Replace all instances of "framework" in the description with one of the following alternatives (choose the most natural fit per sentence):
  • open-source protocol
  • library
  • product
  • infrastructure layer
  • trust layer
• Remove the sentence from the Identity for Things paragraph:

  "The Industry Marketplace provides a perfect example of how this framework and level of autonomy work."

[eike-hass]

done in iotaledger/iota#8283