Specializer SQL support: SELECT * star expansion — corpus 53 → 172 (TASK-46)

[claude-agent-ahrzb]

First rung of the SQL-support push (TASK-46; TASK-47 builtins wave follows separately).

What

Binder::expand_star at the frontend's single projection site — no IR, backend, or boundary changes:

• Plain * and tbl.* in measured DuckDB order (FROM order, declared column order); mixed *, expr items compose naturally.
• EXCLUDE in bare/paren forms, case-insensitive, with DuckDB-mirrored binder errors (unknown column, duplicate entry, exclude-all → empty SELECT).
• Star over a joined static table rejects by name: DuckDB's expansion includes the join-key column and emits duplicate output names there (measured ['k','x','k','y']) — both unrepresentable in a typed output model. __THIS__.* under a join works.
• ILIKE / EXCEPT / REPLACE / RENAME / COLUMNS() reject by name (20 corpus mentions total, macro machinery deferred).

Measured result

• Corpus replay: 53 → 172 match of 678 (+119, 3.2×), zero FAILs. New first-blocker head: BETWEEN 31 · comma join 30 · dynamic-table alias 30 · then the builtin catalogue — TASK-47's target list confirmed.
• Pins: Rust-level expansion tests + duck_check oracle tests (order, EXCLUDE case-folding, join forms, clean rejections).
• Gate green: cargo 129, pytest 627 (13 xfail incl. the pre-existing substr const-fold pin).

Also in this PR: TASK-45 marked Done with final summary; TASK-46/47 tickets created.

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