feat(numbering): publish canonical numbering API

Add a public numbering module and route fragmenting, validation,
and scaffold preparation through the canonical numbering entry.

Rewrite the repository entry docs around the fixed numbering
contract, add MkDocs landing pages, and document the mirror
mapping used for medicinal-chemistry comparisons.

Also refresh the validation analysis reports to explain the
canonical-versus-mirrored numbering relationship.

pixi.toml

@@ -24,3 +24,7 @@ sqlmodel = ">=0.0.37,<0.0.38"
 
 [pypi-dependencies]
 macro_lactone_toolkit = { path = ".", editable = true }
+mkdocs = ">=1.6,<2"
+mkdocs-material = ">=9.6,<10"
+mkdocstrings = ">=0.28,<0.29"
+mkdocstrings-python = ">=1.16,<2"