feat(query): port TextQuery per-token and per-field weights (#17)

[ajGingrich]

Closes #17.

Summary

Brings TS TextQuery to parity with Python redisvl on text weighting:

• textFieldName now accepts string | Record<string, number>.
• New textWeights?: Record<string, number> for per-token bias.
• Renders Redis Search => { $weight: N } syntax (dialect 2).
• All state stays readonly — no mutators (intentional divergence from Python; documented).

Stacked on #31

This PR is based on feat/textquery-stopwords-16 (PR #31, stopwords port). The base branch is set to that PR so GitHub displays a clean diff. Do not merge until #31 lands. I will rebase onto main and undraft once that happens.

Behavior

Input	Renders
textFieldName: 'd'	@d:(quick | fox) (unchanged)
textFieldName: { title: 5 }	@title:(quick | fox) => { $weight: 5 }
textFieldName: { title: 3, body: 1 }	(@title:(quick | fox) => { $weight: 3 } | @body:(quick | fox))
textWeights: { apple: 2 }	@d:(apple=>{$weight:2} | pear)

Tokens are lowercased before textWeights lookup (Python parity, leverages PR #31's normalization pipeline). Parsers use Object.create(null) so adversarial query tokens like constructor or __proto__ cannot resolve through the prototype chain.

What's covered

• src/query/text.ts — widened config, parsers, render logic, JSDoc.
• tests/unit/query/text.test.ts — new tests for field weights, text weights, validation, render output, Python-compat textFieldName getter, prototype-pollution regression.
• tests/integration/query-types.test.ts — multi-field weighted ranking against a real Redis container.
• website/docs/user-guide/filters-and-queries.md — weighting subsection.

Out of scope (intentional)

• Mutators (setFieldWeights, setTextWeights) — TS port stays readonly.
• Stopwords — covered by feat: port TextQuery stopword filtering from Python redisvl (#16) #31.

Verification

npm run lint                   # clean (only pre-existing huggingface warnings)
npm run type-check             # ok
npm run type-check:tests       # ok
npm run test:unit              # 486/486
npm test                       # all green (4 file-level vitest errors from .worktrees/ are pre-existing — not from this branch)
cd website && npm run build    # ok

Test plan

• CI green
• Reviewer confirms render strings against Redis docs (dialect 2 weight syntax)
• Reviewer confirms textFieldName Python-compat getter shape is desired
• Rebase onto main after feat: port TextQuery stopword filtering from Python redisvl (#16) #31 lands; undraft

Reference

Python redisvl: redisvl/query/query.py:1273-1589.

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