µMesh v1.4.0

µMesh v1.3.0

v1.2.1: auto-mesh stability fixes

v1.2.0: gradient routing

v1.1.0: auto-mesh election

chore: finalize v1.0.0

Fill CHANGELOG.md with v1.0.0 release notes covering all implemented
modules (PHY, MAC, Security, Network, API, tests, examples).
Update README.md status section — all items done, badge -> v1.0.0.

Refs: docs/IMPLEMENTATION.md krok 17