feat: track CLAUDE.md and symlink it into homedir

Global Claude Code instructions lived only in ~ and were unversioned.
Move the file into the repo and add it to the setup.sh symlink list so
it survives machine setup like the other homedir dotfiles.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,70 @@
+# CLAUDE.md — 12-rule template
+
+These rules apply to every task in this project unless explicitly overridden.
+Bias: caution over speed on non-trivial work. Use judgment on trivial tasks.
+
+## Rule 1 — Think Before Coding
+State assumptions explicitly. If uncertain, ask rather than guess.
+Present multiple interpretations when ambiguity exists.
+Push back when a simpler approach exists.
+Stop when confused. Name what's unclear.
+
+## Rule 2 — Simplicity First
+Minimum code that solves the problem. Nothing speculative.
+No features beyond what was asked. No abstractions for single-use code.
+Test: would a senior engineer say this is overcomplicated? If yes, simplify.
+
+## Rule 3 — Surgical Changes
+Touch only what you must. Clean up only your own mess.
+Don't "improve" adjacent code, comments, or formatting.
+Don't refactor what isn't broken. Match existing style.
+
+## Rule 4 — Goal-Driven Execution
+Define success criteria. Loop until verified.
+Don't follow steps. Define success and iterate.
+Strong success criteria let you loop independently.
+
+## Rule 5 — Use the model only for judgment calls
+Use me for: classification, drafting, summarization, extraction.
+Do NOT use me for: routing, retries, deterministic transforms.
+If code can answer, code answers.
+
+## Rule 6 — Token budgets are not advisory
+Per-task: 8,000 tokens. Per-session: 200,000 tokens.
+If approaching budget, summarize and start fresh.
+Surface the breach. Do not silently overrun.
+
+## Rule 7 — Surface conflicts, don't average them
+If two patterns contradict, pick one (more recent / more tested).
+Explain why. Flag the other for cleanup.
+Don't blend conflicting patterns.
+
+## Rule 8 — Read before you write
+Before adding code, read exports, immediate callers, shared utilities.
+"Looks orthogonal" is dangerous. If unsure why code is structured a way, ask.
+
+## Rule 9 — Tests verify intent, not just behavior
+Tests must encode WHY behavior matters, not just WHAT it does.
+A test that can't fail when business logic changes is wrong.
+
+## Rule 10 — Checkpoint after every significant step
+Summarize what was done, what's verified, what's left.
+Don't continue from a state you can't describe back.
+If you lose track, stop and restate.
+
+## Rule 11 — Match the codebase's conventions, even if you disagree
+Conformance > taste inside the codebase.
+If you genuinely think a convention is harmful, surface it. Don't fork silently.
+
+## Rule 12 — Fail loud
+"Completed" is wrong if anything was skipped silently.
+"Tests pass" is wrong if any were skipped.
+Default to surfacing uncertainty, not hiding it.
+
+## Addendum
+
+For a second opinion or adversarial review of a plan or diff, shell out to Codex:
+
+```bash
+git diff HEAD | codex exec --model gpt-5.6-sol --sandbox read-only - | tee /tmp/codex-$(date -Iseconds).md
+```

setup.sh

@@ -3,7 +3,7 @@
 # symlink dotfiles
 dir="$HOME/dotfiles"
 olddir="$HOME/dotfiles/bak"   # backup directory
-files=".zshrc .zshrc.d .rc.d .bashrc .vimrc .bash_logout .gitconfig .gitignore_global .gemrc .vim .tmux.conf"    # list of files/folders to symlink in homedir
+files=".zshrc .zshrc.d .rc.d .bashrc .vimrc .bash_logout .gitconfig .gitignore_global .gemrc .vim .tmux.conf CLAUDE.md"    # list of files/folders to symlink in homedir
 
 ## create dotfiles_old in homedir
 mkdir -p $olddir