docs: comprehensive documentation uplift

[cigrainger]

What

Best-in-class documentation for Dux — function groups, rewritten guides with real datasets, cheatsheet overhaul, comprehensive function docs with doctests.

Function documentation

• 43 doctests (up from 37) — every public function in Dux and Dux.Graph now has at least one meaningful doctest
• @doc group: metadata on all 38 public functions: Constructors, Transforms, Aggregation, Joins, Reshape, Sorting, IO, Materialization, Distribution
• Improved docs for: local/1, from_csv/2, from_parquet/2, from_ndjson/2, to_csv/3, to_ndjson/3, ungroup/1, to_tensor/2, head/2, from_edgelist/2, degree/1, vertex_count/1, edge_count/1, triangle_count/1
• Rewrote Dux moduledoc: build → compile → execute lifecycle, quick start with penguins, distribution overview
• Added Dux.Remote moduledoc with Mermaid architecture diagram

Guides (all runnable Livebooks, verified cell-by-cell)

Guide	Dataset	Cells verified
getting-started.livemd	penguins	10/10
data-io.livemd (NEW)	penguins	4/4
transformations.livemd (NEW)	penguins	8/8
joins-and-reshape.livemd (NEW)	nycflights13 star schema	7/7
distributed-queries.livemd	synthetic + workers	verified
graph-analytics.livemd	Zachary's karate club	6/6

Dux.Datasets module

Ships CC0 datasets in priv/datasets/ so guides work with Mix.install:

Dux.Datasets.penguins()    # 344 rows
Dux.Datasets.flights()     # 6,099 rows (nycflights13)
Dux.Datasets.airlines()    # 16 rows
Dux.Datasets.airports()    # 1,458 rows
Dux.Datasets.planes()      # 3,322 rows
Dux.Datasets.gapminder()   # 1,704 rows

Cheatsheet

Complete rewrite with ex_doc features:

• {: .col-2} for macro vs raw SQL side-by-side
• All join types, aggregate functions, DuckDB-specific features
• FLAME in distributed section

ex_doc configuration

• Function grouping via groups_for_docs
• Module groups: Core API (Dux, Query, Datasets), Graph, Distribution (Remote, Coordinator, Worker, Broadcast, Shuffle), Integrations (Telemetry, Flame)
• Mermaid diagram support via before_closing_body_tag
• nest_modules_by_prefix for Dux.Remote.*

Other

• README updated: removed Rust/NIF references, pure Elixir + ADBC
• All module groups correct (fixed Shuffle, Datasets placement)

Test plan

• 43 doctests pass
• 440 total tests, 0 failures
• mix docs builds without errors
• mix credo --strict zero issues
• mix compile --warnings-as-errors clean
• Each guide verified cell-by-cell

🤖 Generated with Claude Code