Stdlib: number_format() for displaying numbers in templates

[PurHur]

Problem

Templates show prices, counts, and stats via number_format($n, 2). Not in capability matrix.

Goal

VM implementation; JIT fast path optional.

Tasks

• ext/standard/number_format.php VM builtin
• PHPT: decimals, thousands separator
• Register in ext/standard/Module.php
• Matrix entry (DevEx: Builtin capability matrix (VM / JIT / AOT per function) #176)

Acceptance criteria

echo number_format(1234.5, 2); → 1,234.50 (locale subset: C-style)

Files

• ext/standard/, docs/capabilities.md