docs: rewrite main README around four principles; retire stale architecture claims - #3588

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-python@v5, astral-sh/setup-uv@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

104:121 [line-length] line too long (122 > 120 characters)

101:121 [line-length] line too long (160 > 120 characters)

84:121 [line-length] line too long (162 > 120 characters)

37:121 [line-length] line too long (124 > 120 characters)

48:121 [line-length] line too long (206 > 120 characters)

179:121 [line-length] line too long (132 > 120 characters)

159:121 [line-length] line too long (189 > 120 characters)

78:121 [line-length] line too long (206 > 120 characters)

34:121 [line-length] line too long (206 > 120 characters)