fix: load tdd.md reference directly in commands

TDD context was only loaded indirectly through workflows.
Now explicitly loaded in plan-phase and execute-plan commands.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

commands/gsd/execute-plan.md

@@ -27,6 +27,7 @@ Uses intelligent segmentation:
 @~/.claude/get-shit-done/workflows/execute-phase.md
 @~/.claude/get-shit-done/templates/summary.md
 @~/.claude/get-shit-done/references/checkpoints.md
+@~/.claude/get-shit-done/references/tdd.md
 </execution_context>
 
 <context>

commands/gsd/plan-phase.md

@@ -25,6 +25,7 @@ Output: One or more PLAN.md files in the phase directory (.planning/phases/XX-na
 @~/.claude/get-shit-done/references/plan-format.md
 @~/.claude/get-shit-done/references/scope-estimation.md
 @~/.claude/get-shit-done/references/checkpoints.md
+@~/.claude/get-shit-done/references/tdd.md
 </execution_context>
 
 <context>