docs: Corrections to Working with models page

[developerjamiu]

Summary

Fact-checked the Working with models page. Three corrections:

• Outdated enum default: The page framed byIndex as the default and recommended setting byName because the default would change "in version 3 of Serverpod." That change has already happened — byName is the default in 3.5.0-beta.4. Reworded the section so it states the current default and warns about byIndex instead.
• distanceFunction keyword row: Listed only l2, innerProduct, cosine, l1, missing jaccard and hamming (used for Bit vectors). Replaced with a pointer to the indexing page, which already documents the full type×index×function matrix.
• Header style: ## Default Values → ## Default values per STYLE_GUIDE.md sentence-case rule. Anchor stays the same.

Test plan

• Render the page locally and confirm the Enum section reads correctly and the keyword table row links work.

[Swiftaxe]

LGTM!