docs: release runbook for the multi-distribution layout

[cayossarian]

Adds RELEASE.md. Nothing recorded how releasing works now that this repo
publishes two PyPI distributions from one source tree, so every release meant
re-deriving it from release.yml.

What it covers

• Layout — which distribution lives where, and the three consequences for
  releasing (own version, own PyPI project, one release publishes one package).
• Why two version axes — the bootstrap versions on its library API, an
  adapter on its library API with the wire format declared by
  SUPPORTS_DATA_MODEL_VERSIONS rather than the version number.
• Tag → distribution → manifest, including the worked parameter-expansion
  example, and why schema-1-v0.1.0 will resolve with no workflow edit.
• Why the tag verifies rather than sets the version, and that the ritual is
  bump-commit-then-tag.
• Releasing one distribution and releasing the whole workspace — the
  latter being the "how does an admin release everything" answer: a sequence of
  single releases, bootstrap first, with the dependency-floor caveat.
• Adding a new adapter — the PyPI pending-publisher table, which is the step
  most likely to be forgotten when schema-1 lands.
• Failure-message table, each string checked against the workflow.
• Verifying from PyPI, since CI going green proves the build and not the
  install — the entry-point seam only exists across a real package boundary.
• Pre-releases — --pre on PyPI, the checkbox on GitHub, and that the
  workflow is indifferent.

Also

• DEVELOPMENT.md gains a workspace-layout section and a pointer to the runbook.
• README install instructions fixed. They still read
  pip install span-panel-api alone, which on this branch gives a client with
  no parser that connects and then raises SpanPanelAdapterMissingError.

Known remaining doc staleness (not addressed here)

The README's Architecture section still describes HomiePropertyAccumulator
and HomieLifecycle as part of this package. They moved to
span_panel_api_schema_0 in Phase 1 and are no longer exported, which the
changelog records but the README contradicts. That is a substantive rewrite of
a section rather than a correction, so it is called out rather than folded in.