feat(vozbox): integrate VOZbox air quality monitors (CCEJN)

[dmpayton]

Summary

• Adds `VOZBox` monitor type for CCEJN's VOZbox devices, which upload CSV data to `QuinnResearch/carbVoz_data` on GitHub
• Implements `VozBoxClient` context manager to download and parse daily/calibration CSVs via the GitHub Contents API and `raw.githubusercontent.com`
• Full LCS PM2.5 pipeline (RAW → CORRECTED → CLEANED → CALIBRATED), dual-channel PM1/PM2.5/PM10, temperature, humidity, and O3
• `O3_VOZBox` calibration processor stub (inactive until a `DefaultCalibration` DB record is created and a model is trained)
• `import_realtime` periodic Huey task (every 10 min) + `process_device` per-device task with dedup and 10-minute downsampling
• `import_vozbox_cal` management command for backfilling externally-calibrated O3 from Quinn Research's cal CSVs
• Django admin with `sensor_id` in list/search/fieldset; add permission disabled (monitors are auto-created on import)
• VOZbox entry in admin sidebar menu
• CCEJN added to the about page Data Providers section
• `VOZBoxHealthCheck` registered at `/system-status/data-feeds/` (30-minute staleness limit)
• `?device=VOZBox` filter supported in both v1 and v2 monitor APIs

Key design decisions

• `VOZBox` inherits `Monitor` directly (not `LCSMixin`) — the device's `coreid` is a 24-char hex string, incompatible with `LCSMixin.sensor_id` (IntegerField)
• O3 `default_stage=CALIBRATED` so external cal entries (with `processor=''`) surface in `LatestEntry` before the internal calibration model is trained
• `_bin_rows()` downsamples incoming rows to 10-minute buckets (earliest row per bucket) before scheduling `process_device` tasks, keeping Redis payloads small even for 1Hz devices
• PM values > 9,999 are dropped (one device uploads bogus readings that overflow the field)
• `get_or_create` used for race-condition-safe monitor creation across concurrent Huey workers
• Supports `GITHUB_API_TOKEN` env var to raise GitHub API rate limits

Test plan

• 41 tests across `VozBoxClientParseTests`, `VozBoxClientHTTPTests`, `VOZBoxModelTests`, `O3VOZBoxProcessorTests`, `ProcessDeviceTests`, `BinRowsTests`, `ImportVozboxCalTests`
• `docker compose run --rm test pytest camp/apps/monitors/vozbox/tests.py -v` — 41 passed
• Manual import confirmed working against live `QuinnResearch/carbVoz_data` (13 devices active)