feat(env): macOS Keychain credential source

Adds the macOS Keychain as the lowest-priority credential source on Darwin.
Items stored as generic passwords with service name "last30days-<KEY>" for
the current user are picked up automatically by get_config() — file env
and process env still win on collision.

No new config knob: behavior is strictly additive. On non-Darwin (or when
the `security` binary is missing) the loader is a no-op, so Linux/Windows
behavior is unchanged.

  Priority (highest wins):
    1. Environment variables
    2. .claude/last30days.env (per-project)
    3. ~/.config/last30days/.env (global)
    4. macOS Keychain items prefixed last30days- (new)

Includes:
  - lib/env.py: KEYCHAIN_SERVICE_PREFIX constant, _load_keychain helper
    (platform-gated, shutil.which-gated, subprocess-error tolerant),
    wiring into get_config before get_openai_auth so OPENAI_API_KEY can
    come from Keychain too, _CONFIG_SOURCE reports "keychain" when no
    file source is present.
  - scripts/setup-keychain.sh: bash helper with interactive set,
    --list, --delete, --replace modes. Uses `security add-generic-password`.
  - tests/test_env_keychain.py: 12 tests covering platform gate,
    missing-binary gate, success path, whitespace stripping, subprocess
    errors swallowed, get_config precedence, and an OPENAI_AUTH wiring
    regression test.
  - tests/test_env_cookies.py: existing integration test mocks the new
    _load_keychain hook so it stays hermetic on Darwin developer
    machines that have real keychain entries.
  - README.md: new "macOS Keychain (optional)" subsection under
    "Bring your own keys" documenting setup-keychain.sh and the manual
    `security add-generic-password` invocation.

Tested on macOS with a populated keychain and against the existing pytest
suite — CI-tracked tests (test_plugin_contract.py, test_version_consistency.py)
plus all env-touching tests pass. Pre-existing unrelated failures in
test_store.py / test_watchlist_commands.py / test_setup_openclaw.py /
test_footer_nudge_suppression.py are untouched.

skills/last30days/scripts/setup-keychain.sh

@@ -0,0 +1,118 @@
+#!/bin/bash
+# Store last30days API keys in the macOS Keychain.
+#
+# Keys are stored as generic passwords with service name `last30days-<KEY>`
+# for the current user. The lib/env.py loader picks them up automatically as
+# the lowest-priority credential source on Darwin.
+#
+# Usage:
+#   ./setup-keychain.sh              # interactive: prompts for each key
+#   ./setup-keychain.sh KEY [KEY..]  # prompt only for the listed keys
+#   ./setup-keychain.sh --list       # list which last30days-* items exist
+#   ./setup-keychain.sh --delete KEY # remove a stored key
+#
+# Existing values are shown as "(set)" and skipped unless --replace is passed.
+# Skip any prompt with empty input.
+
+set -euo pipefail
+
+PREFIX="last30days-"
+ALL_KEYS=(
+  OPENAI_API_KEY
+  XAI_API_KEY
+  GOOGLE_API_KEY
+  GEMINI_API_KEY
+  SCRAPECREATORS_API_KEY
+  APIFY_API_TOKEN
+  AUTH_TOKEN
+  CT0
+  BSKY_HANDLE
+  BSKY_APP_PASSWORD
+  TRUTHSOCIAL_TOKEN
+  BRAVE_API_KEY
+  EXA_API_KEY
+  SERPER_API_KEY
+  OPENROUTER_API_KEY
+  PARALLEL_API_KEY
+  XQUIK_API_KEY
+)
+
+if [[ "${OSTYPE:-}" != darwin* ]]; then
+  echo "setup-keychain.sh requires macOS (security command). Got: $OSTYPE" >&2
+  exit 1
+fi
+if ! command -v security >/dev/null 2>&1; then
+  echo "security command not found on PATH" >&2
+  exit 1
+fi
+
+REPLACE=0
+ACTION="prompt"
+TARGETS=()
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --list) ACTION="list"; shift ;;
+    --delete) ACTION="delete"; shift ;;
+    --replace) REPLACE=1; shift ;;
+    --help|-h) sed -n '2,/^$/p' "$0" | sed 's/^# //; s/^#//'; exit 0 ;;
+    -*) echo "unknown flag: $1" >&2; exit 2 ;;
+    *) TARGETS+=("$1"); shift ;;
+  esac
+done
+
+case "$ACTION" in
+  list)
+    echo "Stored last30days-* keychain items:"
+    for key in "${ALL_KEYS[@]}"; do
+      if security find-generic-password -a "$USER" -s "${PREFIX}${key}" -w >/dev/null 2>&1; then
+        echo "  $key"
+      fi
+    done
+    exit 0
+    ;;
+  delete)
+    if [[ ${#TARGETS[@]} -eq 0 ]]; then
+      echo "--delete needs at least one KEY name" >&2; exit 2
+    fi
+    for key in "${TARGETS[@]}"; do
+      if security delete-generic-password -a "$USER" -s "${PREFIX}${key}" >/dev/null 2>&1; then
+        echo "deleted: $key"
+      else
+        echo "not found: $key"
+      fi
+    done
+    exit 0
+    ;;
+esac
+
+if [[ ${#TARGETS[@]} -eq 0 ]]; then
+  TARGETS=("${ALL_KEYS[@]}")
+fi
+
+added=0; skipped=0; replaced=0
+for key in "${TARGETS[@]}"; do
+  existing="$(security find-generic-password -a "$USER" -s "${PREFIX}${key}" -w 2>/dev/null || true)"
+  if [[ -n "$existing" && "$REPLACE" -eq 0 ]]; then
+    printf "  %-28s (set, skipping — use --replace to overwrite)\n" "$key"
+    skipped=$((skipped + 1))
+    continue
+  fi
+  printf "  %-28s " "$key"
+  IFS= read -rs value
+  echo
+  if [[ -z "$value" ]]; then
+    skipped=$((skipped + 1))
+    continue
+  fi
+  security add-generic-password -U -a "$USER" -s "${PREFIX}${key}" -w "$value"
+  if [[ -n "$existing" ]]; then
+    replaced=$((replaced + 1))
+  else
+    added=$((added + 1))
+  fi
+done
+
+echo
+echo "Done. added=$added replaced=$replaced skipped=$skipped"
+echo "Verify with: $0 --list"