docs: Standardize all IndieAuth spec references to W3C URL

- Updated 42 references from indieauth.spec.indieweb.org to www.w3.org/TR/indieauth
- Ensures consistency across all documentation
- Points to the authoritative W3C specification
- No functional changes, documentation update only

Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

docs/architecture/technology-stack.md

@@ -725,7 +725,7 @@ Return success
 **Token Format**: Bearer tokens
 **Validation**: Token introspection
 
-**Reference**: https://indieauth.spec.indieweb.org/
+**Reference**: https://www.w3.org/TR/indieauth/
 
 #### Micropub
 **Compliance**: Full Micropub spec support
@@ -1061,7 +1061,7 @@ This stack embodies the project philosophy: "Every line of code must justify its
 
 ### Standards and Specifications
 - IndieWeb: https://indieweb.org/
-- IndieAuth Spec: https://indieauth.spec.indieweb.org/
+- IndieAuth Spec: https://www.w3.org/TR/indieauth/
 - Micropub Spec: https://micropub.spec.indieweb.org/
 - Microformats2: http://microformats.org/wiki/h-entry
 - RSS 2.0: https://www.rssboard.org/rss-specification