Start Housecarl: the logo, the wordmark and the skeleton

Housecarl will be a firewall manager for nftables, built the way Jarl and
Steward are: housecarld (a daemon with a REST API and web UI), hc (the
CLI) and SQLite.

- The logo: a carved Nordic doorway in Jarl's blue (artwork/logo.svg),
  with a small version without the carvings, lighter on dark
  backgrounds. scripts/logo.py builds the web UI's copies and
  scripts/banner.py the README banner.
- The HOUSECARL wordmark in Jarl's and Steward's angular letters, with
  new H, O, U and C (assets/brand.js), and the UI's color tokens.
- housecarld and hc print their version; the Makefile, version package,
  AGENTS.md, CHANGELOG and the design sketch (docs/design.md).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,19 @@
+# Changelog
+
+All notable changes to Housecarl are documented here. The format follows
+[Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and versions follow
+[Semantic Versioning](https://semver.org/).
+
+## [Unreleased]
+
+The start of Housecarl, a firewall manager for nftables, built the way
+Jarl and Steward are.
+
+### Added
+
+- **The Housecarl logo:** a carved Nordic doorway in Jarl's blue, with a
+  simplified version for small sizes, lighter on dark backgrounds; and a
+  HOUSECARL wordmark in Jarl's and Steward's angular letters.
+- **The skeleton:** the `housecarld` daemon and the `hc` CLI (both only
+  print their version), the build, and the design sketch
+  (docs/design.md).