docs: explore-minimax memory + ask-minimax usage update

Add /explore-minimax and explore-minimax-run memory files, backfill
skill-ask-minimax / skill-ask-minimax-with-context entries, index them in
MEMORY.md. ask-minimax-usage.md gains the exploration use case and an
explicit no-secrets rule.

Claude-Session: https://claude.ai/code/session_01Ku87DDWwbJkTx6SuV3sQDc

claude/ask-minimax-usage.md

@@ -9,6 +9,7 @@
 - Generating big files (migrations, config bundles, fixtures, large docs) where the content does not need to flow back
 - Format conversion of large files (CSV↔JSON, XML↔YAML, etc.)
 - Bulk find-and-extract across many files where only the matches matter
+- Broad read-only codebase exploration ("where does X live", "how is Y wired up") — use the specialised `/explore-minimax` skill, which enforces read-only, requires `file:line` citations, and falls back to the Explore agent on failure
 
 ## Skip it for
 
@@ -17,6 +18,7 @@
 - Tasks where you will immediately re-read the result to act on it
 - Anything requiring tools MiniMax cannot use (web fetch, MCP, browser, agent dispatch)
 - Architecture or quality-sensitive output — MiniMax is for grunt work, not nuanced reasoning
+- Anything touching `secrets/`, `local_secrets/`, or credential material — never hand secret-adjacent paths to a third-party model
 
 ## How to delegate