Restructure docs around conversational role dispatch

[antoinezambelli]

Summary

• rewrite the README as a concise human entry point: what/why, install, use, and durable evidence
• center the primary usage pattern on a Sol conversation dispatching cheaper Terra/Luna roles through codex-exec-subagents
• move installation, direct CLI usage, and security/retention detail into dedicated documents
• retain the concrete receipt example in the artifact-lifecycle contract
• ship the new documents in the source distribution and update documentation/package coverage

Validation

• fast suite: 131 passed, 24 deselected
• focused wheel/sdist integration: 2 passed, 15 deselected
• documentation suite: 19 passed
• wheel and sdist: twine check --strict passed
• PyPI Markdown rendering: valid HTML, expected heading structure, 16 valid links, no malformed or unintended relative links
• git diff --check passed