Per-user weighted word statistics

### Describe the problem

Weblate’s current reporting shows basic counts of words/characters and contributions per user, but these are unweighted and do not include CAT-style categories such as repetitions, fuzzy matches, match percentages, or weighted effort.

This limits visibility into actual translation effort compared to tools like memoQ, which break down word counts by match type and apply weighted metrics to better reflect the workload

### Solution brainstorm

Add an optional report or API that produces per-user, weighted word statistics using match categories (e.g., no match, fuzzy ranges, exact matches, repetitions) similar to what CAT tools provide. These statistics could:

- Surface effort-based metrics beyond raw word counts,
- Enable fairer reporting per contributor,
- Serve as a more accurate input for cost estimation (e.g., in #7389).

This would build on Weblate’s existing reporting while extending it to include weighted, match-aware metrics.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

_No response_