docs: Datalog tutorial series — 11 sections, Corestore storyline (closes #234)

[adityamukho]

Summary

• Adds demos/tutorial_corestore_setup.txt — the shared base dataset (Corestore e-commerce catalog: 3 categories, 8 products, 3 customers) that all 11 tutorial sections build on
• Adds examples/tutorial_udfs.rs — a standalone Rust example demonstrating register_predicate and register_aggregate (Section 10, UDF-only features that cannot be shown in the REPL)
• Delivers 12 wiki pages (setup + 11 sections) covering every Minigraf Datalog grammar construct, driven by a real-world e-commerce storyline (Corestore, with characters Alice/Ben/Clara)

Wiki pages published:

• Tutorial-Setup — prerequisites, dataset, cumulative tx_count table
• Tutorial-01 through Tutorial-11 — basic queries → bi-temporal → recursion → negation → aggregates → expressions → prepared queries → disjunction → UDFs → marketplace
• Home.md — "Tutorials" section added before "Pages"
• Learning-Resources.md — tutorial series listed as primary Minigraf Datalog resource

Grammar coverage

All constructs from Datalog-Reference.md are demonstrated: transact, retract, rule, query, :find (variables, aggregates, window exprs), :where (pattern, expr, not, not-join, or, or-join, and-branch, rule-invocation), :as-of, :valid-at, :any-valid-time, :with, scalar aggregates, window functions, :partition-by, :order-by, :desc, comparison/arithmetic/string/type predicates, $bind-slot prepared queries, register_predicate UDF, register_aggregate UDF.

Test plan

• cargo run --example tutorial_udfs produces the expected predicate + aggregate + window output
• cargo run < demos/tutorial_corestore_setup.txt loads 3 transacts cleanly (tx_count = 3)
• All 795 existing tests continue to pass (verified by pre-push hook above)
• Wiki pages render correctly on https://github.com/project-minigraf/minigraf/wiki

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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