Add best practices, hooks, memory files, and scripts from recent sessions

Includes: spec-driven and test-driven development best practices,
reproduce-before-fixing debugging workflow, require-plan-file hook,
find-project-root script, session logs, memory files for decisions/
gotchas/process-lessons, and updates to existing best practice topics.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hooks/require-plan-file.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+# Blocks ExitPlanMode unless a *-PLAN.md file exists in the current working directory.
+# Fired via PreToolUse hook on ExitPlanMode.
+# Input: JSON on stdin with session context including "cwd".
+
+INPUT=$(cat)
+CWD=$(echo "$INPUT" | python3 -c "import sys, json; print(json.load(sys.stdin).get('cwd', ''))" 2>/dev/null)
+
+if [ -z "$CWD" ]; then
+    exit 0  # Can't determine cwd, allow through
+fi
+
+if ls "$CWD"/*-PLAN.md 2>/dev/null | grep -q .; then
+    exit 0  # Plan file exists, allow exit
+fi
+
+echo "No PLAN.md file found in $CWD. Before exiting plan mode, write the complete plan to a file named [MILESTONE]-[PURPOSE]-PLAN.md in the project root (e.g. M2-auth-PLAN.md)." >&2
+exit 2