fix(minimax-m3-max, fable-low-effort): requires takes harness refs, not capability tags

'requires: [claude-code]' failed composition ('Invalid harness reference
format'). Both contexts need no hard dependency — layer ordering in the
composites already guarantees the auth layer precedes them. Validated
locally with entrypoint.harness compose_harness for all 6 affected
composites this time.

Claude-Session: https://claude.ai/code/session_019tJk7P8tZzJ24PvtgoGhLN

harnesses/contexts/minimax-m3-max/v1/harness.yaml

@@ -2,7 +2,7 @@ kind: context
 name: minimax-m3-max
 version: 1
 description: "Pin MiniMax M3 (1M context) at max reasoning effort — layer AFTER minimax/v1 (auth + base URL come from there)"
-requires: [claude-code]
+requires: []
 provides: []
 
 # Model pin + effort for the MiniMax Anthropic-compatible proxy.