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>

.reflection-state.json

@@ -0,0 +1,9 @@
+{
+  "version": 1,
+  "last_run": "2026-03-15T09:25:01Z",
+  "processed": {
+    "log/2026-03-12.233744.md": "ca482f03914a3b4dec89c2dbf6e0f2e5",
+    "log/2026-03-13.100758.md": "65c5b65fdd5984c036f1de53f8c82f2a",
+    "log/2026-03-13.115251.md": "56a27d18deeb89c8ce8b112b099ac7cf"
+  }
+}