v1.9.3

The content that was waiting under "Unreleased" is now versioned (patch,
documentation only, consistent with GatewayLab's history).

Changed

• Documentation refactored. The README carried the whole reference (REST API, feature table, identification sources, structure, web workflow). It is trimmed to a concise overview; the reference moves into dedicated documents: docs/API.md (REST API), docs/FEATURES.md (features), docs/PROTOCOLS.md (identification sources). Structure and web pipeline stay in docs/ARCHITECTURE.md.
• Bilingual README. README.md (English) and README.fr.md (French) are now present and mirror each other, with the language toggle line and the version badge.

Note: the previous version 1.9.2 ("three OUIs added to the vendor table": 00:51:ED, B0:19:21 TP-Link; CC:7B:5C Xsens) may never have been tagged. If so, create v1.9.2 from its CHANGELOG entry as well, before v1.9.3.