feat: add skill cross-references for discoverability

- Reference preserving-productive-tensions from brainstorming EXPLORING mode
- Reference detecting-emergent-patterns from brainstorming when stuck
- Reference tracing-knowledge-lineages from brainstorming before changes
- Reference tracing-knowledge-lineages from executing-plans REVIEWING mode

Makes new architecture skills discoverable through commonly-used workflows.

skills/collaboration/brainstorming/SKILL.md

@@ -77,6 +77,15 @@ When your partner confirms (any affirmative response):
 - Switch to skills/collaboration/writing-plans skill
 - Create detailed plan in the worktree
 
+## Related Skills
+
+**During EXPLORING mode:**
+- When approaches have genuine trade-offs: skills/architecture/preserving-productive-tensions
+- When stuck or seeking innovation: skills/architecture/detecting-emergent-patterns
+
+**Before proposing changes:**
+- Understand why current approach exists: skills/architecture/tracing-knowledge-lineages
+
 ## Remember
 
 - Modes are operational stances, not linear phases

skills/collaboration/executing-plans/SKILL.md

@@ -22,7 +22,7 @@ digraph executing_modes {
     rankdir=LR;
     node [shape=box, style=rounded];
 
-    REVIEWING [label="REVIEWING Mode\n\nRead plan critically\nIdentify concerns/questions/gaps\nCreate TodoWrite if plan is sound"];
+    REVIEWING [label="REVIEWING Mode\n\nRead plan critically\nIdentify concerns/questions/gaps\nConsider skills/architecture/tracing-knowledge-lineages\nCreate TodoWrite if plan is sound"];
 
     EXECUTING [label="EXECUTING Mode\n\nWork through batch (default 3 tasks)\nFollow each step exactly\nRun all verifications\nMark tasks completed"];