feat(agg): BIT/BOOL aggregates + FIRST_VALUE/LAST_VALUE/NTH_VALUE window helpers

[productdevbook]

Summary

Adds eight typed builders for SQL aggregate and window functions that were missing from the public surface:

• BIT aggregates — bitAnd, bitOr, bitXor (PG/MySQL/SQLite 3.44+ for AND/OR; MySQL-only for XOR)
• BOOL aggregates — boolAnd, boolOr (PG and SQLite 3.45+; MySQL/MSSQL refuse — workaround is MIN/MAX(CAST(b AS int)))
• Window-value helpers — firstValue, lastValue, nthValue (window-only — already in WINDOW_ONLY_FUNCTIONS; previously callers had to reach for sqlFn)

Per-dialect gating goes through four new feature flags (BIT_AGGREGATES, BIT_XOR_AGG, BOOL_AGGREGATES, NTH_VALUE_FN). Printer overrides surface the matrix at compile time so unsupported combos throw UnsupportedDialectFeatureError instead of leaking through to a runtime "no such function" parse error.

PG: also gates BIT_XOR (PG 14+ does ship it natively, but older PG versions surface a UDF-lookup error — PG 14+ users can bypass via sqlFn("BIT_XOR", expr)).

Files

• src/builder/aggregate.ts — 8 new builders, all JSDoc-annotated with the dialect matrix and the LAST_VALUE frame-default footgun
• src/dialect/features.ts — 4 new feature entries
• src/printer/function-tables.ts — adds BIT_/BOOL_ to STANDARD_FUNCTIONS
• src/printer/{pg,mysql,sqlite,mssql}.ts — gating overrides
• src/builder/eb.ts, src/index.ts, src/ns/win.ts — re-exports (window helpers also mirrored into the win namespace alongside lag/lead)
• docs/recipes.md — new subsections for bitwise/boolean aggregates and window-value functions

Test plan

• pnpm fmt && pnpm lint && pnpm typecheck && pnpm vitest run — 2458 passed
• test/builder/bit-bool-aggregates.test.ts — SQL output across all four dialects, refusal checks, PGlite roundtrip verifying the actual fold result
• test/builder/window-value-fns.test.ts — SQL output, OVER-required check, MSSQL NTH_VALUE refusal, win namespace mirror, PGlite roundtrip for opening/closing/Nth values

Tradeoffs

• BIT_XOR_AGG lists only MySQL even though PG 14+ has the function. sumak has no per-version gating today; the safe default is "refuse" with an sqlFn escape hatch documented in the JSDoc. Following the same pattern as the trigonometry feature flag.
• BOOL_AND / BOOL_OR could have a portable rewrite to MIN(CAST(b AS int)) on MySQL/MSSQL but the result type and NULL semantics differ subtly (boolean vs int). Refuse + document the workaround keeps the builder surface honest.
• firstValue/lastValue/nthValue are documented as window-only and the printer already enforces it via the existing WINDOW_ONLY_FUNCTIONS allowlist — no new gating needed for the OVER-required check.

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