feat: add core/ tier reflecting actual universal workflow

The original repo presented everything as equal rules. In reality, the
workflow has two tiers: core practices (used in every project) and advanced
rules (only in complex projects like Mortdecai).

Core tier adds:
- backup-before-edit (global CLAUDE.md rule)
- superpowers-workflow (the actual workflow engine)
- memory-system (persistent feedback and project memories)
- document-hierarchy (CLAUDE.md/SESSION.md/CONTEXT.md/IDEA.md)
- commit-and-push discipline
- feedback-driven behaviors

Updated README, docs, and dynamic-methodology to reflect the two-tier
reality instead of presenting advanced rules as universal.

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

core/backup-before-edit.md

@@ -0,0 +1,41 @@
+# Backup Before Edit
+
+Before editing any file, back up the original to a `.backup/` directory in the same parent folder.
+
+## Why
+
+Disk space is cheap. Lost work is expensive. AI assistants sometimes make destructive edits — overwriting files, truncating content, or introducing bugs that are hard to reverse. A `.backup/` directory provides instant recovery without relying on git history (which may not exist yet, or may have uncommitted changes).
+
+## How
+
+Before modifying `src/config.py`:
+
+```bash
+mkdir -p src/.backup
+cp src/config.py src/.backup/config.py
+```
+
+For files that get edited multiple times, timestamp the backup:
+
+```bash
+cp src/config.py src/.backup/config.py.$(date +%Y%m%d-%H%M%S)
+```
+
+## Gitignore
+
+Add `.backup/` to your `.gitignore` so backups are never committed:
+
+```
+.backup/
+```
+
+## When to Apply
+
+- **Always** before editing existing files, especially configuration or infrastructure files
+- **Always** when an AI assistant is making changes to files you haven't read yet
+- **Skip** for files you just created in this session (nothing to back up)
+- **Skip** for test files during rapid iteration (git handles recovery)
+
+## Where This Rule Lives
+
+This belongs in your global `~/.claude/CLAUDE.md` so it applies to every project without per-project configuration. It's the one rule that should be universal and unconditional.