docs: rebrand messaging — 'the self-improving AI agent'

- Lead with the learning loop: autonomous skill creation, skill
  self-improvement, memory nudges, FTS5 session search, Honcho
  dialectic user modeling
- 'Runs anywhere' angle: 6 backends, serverless persistence with
  Daytona/Modal, not tied to your laptop
- 'Built by model trainers' replaces 'model-agnostic'
- Updated README tagline, feature table, subtitle
- Updated docs landing page hero, description, key features
- Updated docusaurus tagline and pyproject.toml description

website/docusaurus.config.ts

@@ -4,7 +4,7 @@ import type * as Preset from '@docusaurus/preset-classic';
 
 const config: Config = {
   title: 'Hermes Agent',
-  tagline: 'An AI agent that grows with you',
+  tagline: 'The self-improving AI agent',
   favicon: 'img/favicon.svg',
 
   url: 'https://hermes-agent.nousresearch.com',