[fix] correct typos / wrong examples / mislabeled params in aggregate, AI, and array function docs

[boluor]

Summary

Fixes 13 small documentation issues across the aggregate, AI, and array function references. Each item below is independent.

• stddev.md — Return Value said "sample standard deviation", but STDDEV / STDDEV_POP compute the population standard deviation (STDDEV_SAMP is the sample variant). Corrected the English and Chinese copies.
• inner-product-approximate.md / inner-product.md / array-cross-product.md — the Parameters table labeled the second-row parameter as \`. Changed to ``` to match the function signature.
• inner-product-approximate.md — the example query called L2_distance_approximate(embedding, ...) (the function being documented is INNER_PRODUCT_APPROXIMATE). Changed the call to inner_product_approximate(...).
• ai-summarize.md / ai-translate.md — typo 'resourse_name' → 'resource_name'.
• ai-classify.md — sample label 'useage' → 'usage'.
• array-avg.md — the "Array is NULL" example called array_max(NULL) (looked like a copy-paste from array-max.md). Changed to array_avg(NULL).
• array-product.md — example array_product([1.1, 2.2, 3.3, 4.4, 5.5]) showed a result of 190.8. The actual product is 193.2612.
• array-reverse-split.md / array-split.md — result string [[1,[NULL,3]] had mismatched brackets; corrected to [[1, NULL, 3]].
• array-union.md — the result-table header for a 3-element query (ARRAY('hello', 'world', 'hello')) showed only 2 elements. Header now matches the query; ruler and right-edge padding widened to keep the table aligned.

Test plan

• CI doc build passes
• Spot-check that the affected function pages render correctly (parameter tables in inner-product / inner-product-approximate / array-cross-product, the corrected query in inner-product-approximate, the fixed value in array-product, the corrected result strings in array-reverse-split / array-split, and the realigned table in array-union)