wiki: fix malformed backlinks across all articles

Batch-replace [[wiki/clients/slug.md]] → [[clients/slug]] format
throughout overview.md and 6 client articles. The seeding agents used
the full path+extension format; correct convention is type/slug only.

Also fixes [[projects/msp-tools/guru-rmm]] → [[projects/gururmm]]
stale path in internal-infrastructure.md.

Post /wiki-lint run: 0 remaining format violations, 2 legitimate
broken links left (systems/neptune — unseeded; compilation queue entry).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

wiki/clients/khalsa.md

@@ -170,5 +170,5 @@ No issue log entries. No session logs exist for this client.
 
 ## Backlinks
 
-- [[wiki/index]] — client index
-- [[wiki/patterns/apple-domain-join]] — if a general Apple domain join pattern article exists or is created
+- [[index]] — client index
+- [[patterns/apple-domain-join]] — if a general Apple domain join pattern article exists or is created