chore: install refactoring guardrails (Phase 0) [guardrail-change]

- scripts/check-loc.sh: LOC budget checker (500 LOC hard cap)
- .claude/rules/architecture.md: split triggers, patterns per language
- .claude/rules/loc-exceptions.txt: documented escape hatches
- AGENTS.python.md: FastAPI conventions (routes thin, service layer)
- AGENTS.go.md: Go/Gin conventions (handler ≤40 LOC)
- AGENTS.typescript.md: Next.js conventions (page.tsx ≤250 LOC, colocation)
- CLAUDE.md extended with guardrail section + commit markers

273 files currently exceed 500 LOC — to be addressed phase by phase.

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

scripts/check-loc.sh

@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+MAX_LOC="${MAX_LOC:-500}"
+ROOT_DIR="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
+EXCEPTIONS_FILE="${ROOT_DIR}/.claude/rules/loc-exceptions.txt"
+
+red()   { printf '\033[31m%s\033[0m\n' "$*"; }
+green() { printf '\033[32m%s\033[0m\n' "$*"; }
+
+is_exempt() {
+  local file="$1"
+  [[ -f "$EXCEPTIONS_FILE" ]] || return 1
+  while IFS= read -r line; do
+    [[ -z "$line" ]] && continue
+    [[ "$line" =~ ^# ]] && continue
+    local pattern="${line%%|*}"
+    pattern="$(echo "$pattern" | xargs)"
+    if [[ -n "$pattern" ]] && [[ "$file" == $pattern ]]; then
+      return 0
+    fi
+  done < "$EXCEPTIONS_FILE"
+  return 1
+}
+
+count_loc() {
+  [[ -f "$1" ]] && awk 'END { print NR }' "$1" || echo 0
+}
+
+collect_changed_files() {
+  { git diff --name-only --cached; git diff --name-only; git ls-files --others --exclude-standard; } | awk 'NF' | sort -u
+}
+
+main() {
+  local mode="changed"
+  [[ "${1:-}" == "--changed" ]] && mode="changed"
+  [[ "${1:-}" == "--all" ]] && mode="all"
+
+  local files=()
+  if [[ "$mode" == "changed" ]]; then
+    IFS=$'\n' read -d '' -r -a files < <(collect_changed_files)
+  else
+    IFS=$'\n' read -d '' -r -a files < <(find "$ROOT_DIR" \( -name '*.py' -o -name '*.go' -o -name '*.ts' -o -name '*.tsx' \) -not -path '*/node_modules/*' -not -path '*/.next/*' -not -path '*/__pycache__/*' -not -path '*/venv/*')
+  fi
+
+  local failed=0
+  local violations=0
+
+  for file in "${files[@]}"; do
+    [[ -f "$file" ]] || continue
+    is_exempt "$file" && continue
+    local loc
+    loc="$(count_loc "$file")"
+    if (( loc > MAX_LOC )); then
+      red "VIOLATION: $file ($loc LOC > $MAX_LOC)"
+      violations=$((violations + 1))
+      failed=1
+    fi
+  done
+
+  if (( failed )); then
+    red ""
+    red "$violations file(s) exceed ${MAX_LOC} LOC budget."
+    exit 1
+  fi
+
+  green "LOC budget check passed."
+}
+
+main "$@"