feat: field projection and output normalisation

[miichom]

This update adds field‑level selection and makes output behaviour more consistent. Missing selectors now return undefined, and pages that fail to load return null. Array fields no longer default to empty arrays when their selectors are not present, making it easier to tell the difference between “no data found” and “no selector available”.

Example:

// Before
{ pvpteam: { id: undefined, name: undefined, crest: [] }, ... }

// After
{ pvpteam: { id: undefined, name: undefined, crest: undefined }, ... }

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🟠	Lines	86.59%	84 / 97
🟠	Statements	82.72%	91 / 110
🟢	Functions	94.73%	18 / 19
🔴	Branches	67.74%	63 / 93

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/lib/endpoint.ts	81%	67.39%	94.44%	85.05%
src/lib/registry.ts	100%	100%	100%	100%

Generated in workflow #16 for commit b19c31c by the Vitest Coverage Report Action