Refactor telemetry backend to store all telemetry in a single collection and add repo_source-based filtering.
Key changes:
- Added detect_repo_source() in misc/api.func to auto-detect/export REPO_SOURCE (ProxmoxVE/ProxmoxVED/external) when scripts are sourced.
- Consolidated PocketBase collections into a single default collection (_telemetry_data) across service, migration, and scripts; updated defaults in migrate.go, migration.go, migrate.sh and migration shell scripts.
- Simplified PBClient to use one targetColl and removed collection resolution logic; updated create/update/find/fetch functions to use targetColl.
- Introduced repo_source field (values: "ProxmoxVE", "ProxmoxVED", "external") on telemetry records and telemetry payloads; updated validation and logging.
- Added repo filtering to dashboard endpoints, FetchDashboardData and FetchRecordsPaginated, plus a repo selector in the dashboard UI; default filter is ProxmoxVE (production), with an "all" option.
- Adjusted API handlers and callers to pass repo filters and include repo_source when upserting telemetry.
- Misc: updated comments, error messages, and logging to reflect the new model; added telemetry-service.exe binary.
Purpose: simplify data model (single collection), make telemetry attributable to repository sources, and enable dashboard filtering by repo/source.
