contacts: extract into standalone skill, add himalaya wrapper for all email sends

Refactors the contacts system from being embedded in cal_tool.py into a
standalone contacts skill that serves as the single source of truth for
recipient validation across all outbound email paths.

- New skills/contacts/ skill: list, add, delete, resolve commands
- New skills/himalaya/scripts/himalaya.sh wrapper: validates To/Cc/Bcc
  recipients against contacts for message send, template send, and
  message write commands; passes everything else through unchanged
- cal_tool.py now delegates to contacts.py resolve instead of inline logic
- TOOLS.md updated: agent should use himalaya wrapper, not raw himalaya

skills/contacts/scripts/contacts.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# contacts — manage the local contact list (vCard / CardDAV).
+#
+# Usage:
+#   ./contacts.sh list                          # list all contacts
+#   ./contacts.sh add [options]                 # add a contact
+#   ./contacts.sh delete [options]              # delete a contact
+#   ./contacts.sh resolve <name|name:type|email> # resolve to email address
+#
+# No external dependencies (pure Python 3).
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+
+exec python3 "$SCRIPT_DIR/contacts.py" "$@"