[Kinflou]

Docs for comline-typescript#32, plus two things from already-merged CLI work that never reached the docs.

lib mode

library-generation.md said lib was "rust only" and that "a schema
whose namespace is nested (a/b)" was "not done yet". Both stale: rust's
ModuleTree has handled nested namespaces all along, and typescript now
does too. The lib section gains a typescript half — the package shape, the
index.ts-per-level barrel and why it mirrors namespaces instead of
flattening (std is implicit in every package, so a flat barrel makes your
own Request ambiguous with std/http's, which TypeScript refuses
outright), and the one restriction both generators share: a namespace can be
a schema or a parent of deeper schemas, not both.

Cross-schema references

generating-code.md only documented rust's crate::-qualified paths. Added
the typescript equivalent — import type by relative specifier, aliases
importing the name the other module exports, unused uses producing
nothing — along with the assumption that carries: code mode needs the
layout to keep each namespace in the file-name position. Every layout
the docs show does, including the default.

Flags that were never documented

scripts/check-cli-drift.py was failing on main:

`comline generate`
  + --no-external-std    in the CLI, not in the docs

--no-external-std (cli#58) was missing from cli.md entirely, and
--dry-run was in the flag list but unexplained. Both documented, and the
external_std default is now stated (on in lib, off in code). The drift
check is clean again:

No drift: the docs match comline 0.2.0.

The [[generate.target]] section also still described a block as what
decides whether a language is generated — the behaviour cli#59 fixed — so
that carries over here too.

Both drift scripts pass. mkdocs isn't installed locally, so the site build is
unverified.