fix(sql-editor): fail closed on incomplete @set captures

[cursor]

Bug and impact

-- @set name = column … / -- @set name = table could capture only the current result page (or silently trim to the 500-row/value cap) while still succeeding. Later ${{…}} expansion then ran against a partial variable with no error — e.g. DELETE … WHERE id IN (${{ids}}) missing most IDs when Max rows/page was smaller than the SELECT.

Root cause

applySetDirectives ignored hasNext / truncated from paged SQL results and sliced list/table payloads to the variable caps without failing.

Fix

• Fail closed for column/table @set when the result is incomplete (hasNext or truncated) or would exceed the list/table caps.
• Scalar @set still allows a partial page (only the first cell is used).

Validation

• Added unit tests for incomplete-page and over-cap refusal.
• npx vitest run apps/web/src/frontend/lib/sql-variables.test.ts — 28 passed.