Support Dreeve self-host weight

[sanglt]

Summary

Adds a direct Dreeve exporter for BLE Scale Sync.

Dreeve now exposes a bearer-authenticated athlete-weight API. This exporter sends BLE Scale Sync readings directly to a self-hosted Dreeve instance, without requiring an Android/openScale-sync intermediary.

The exporter is deliberately weight-only because Dreeve currently accepts only weight measurements.

This exporter targets the athlete-weight API introduced in
dreeveapp/dreeve#2653.

Changes

• Added a dreeve exporter with:
  • POST /api/v1/athlete/weights delivery.
  • Bearer-token authentication using a Dreeve drv_... API key.
  • GET /api/v1/status health check.
  • Historical-reading support using the original local calendar date.
  • Existing shared HTTP retry behavior: retries transient failures and fails fast for non-retryable 4xx responses.
• Added required Dreeve exporter configuration:
  • base_url
  • token
  • unit_system
• Added explicit unit_system: metric | imperial handling:
  • BLE Scale Sync measurements remain internally normalized to kilograms.
  • metric sends kilograms.
  • imperial converts kilograms to pounds before sending.
  • The setting is required so an Imperial Dreeve instance cannot silently store kilogram readings as pounds.
• Registered Dreeve in the exporter registry, factory, setup wizard, and legacy .env configuration path.
• Added Dreeve examples and documentation to config.yaml.example, .env.example, exporter docs, README, site landing page, FAQ, and exporter-count metadata.
• Updated exporter count from 11 to 12.

Test Plan

• Tests pass (npm test)
• Lint clean (npm run lint)
• TypeScript compiles (npx tsc --noEmit)
• Tested manually (describe below)

Focused verification also passed:

• Dreeve exporter/configuration/registry tests: 158 tests passed.
• Dreeve exporter coverage: 100% statements, branches, functions, and lines.
• Prettier check passed.
• VitePress documentation build passed.
• Exporter-count check passed.
• git diff --check passed.

Manual verification was not performed against a live Dreeve instance. HTTP contract tests cover the documented status and weight endpoints, bearer authorization, metric and Imperial payloads, retry behavior, date handling, and error handling.

Notes

• This is an export-only, weight-only integration. Dreeve does not currently expose endpoints for body fat, water, muscle mass, bone mass, or other body-composition values.
• Dreeve stores one weight measurement per calendar date. A later reading for the same date replaces the earlier value.
• unit_system must match the Dreeve instance Appearance setting exactly:
  • metric for kilograms.
  • imperial for pounds.
• The Dreeve API must be enabled with DREEVE_API_KEY, and the same generated drv_... key must be configured as the exporter token.