Breeze Core v3.0.0 (prerelease 2)

Prerelease 2 of the v3.0.0 overhaul — from the overhaul branch, for testing. Not on the bolero repo (stable only).

Everything in pre1 (Ed25519 request signing, scan-to-add, opt-in beep) plus:

• Live push over SSE — GET /api/units/stream: the server polls the units centrally (only while a client is connected) and pushes state changes, so the app can drop its own polling. Emits event: state frames + keepalives; compression forced off and X-Accel-Buffering: no so it streams cleanly through proxies.
• Per-unit capabilities — GET /api/units/{id}/capabilities: what the hardware supports (modes, flap axes, eco/turbo, temp range, …) so clients hide controls a unit lacks.
• whoami — GET /api/auth/whoami: the calling device's own record (label, auth version, expiry).
• History + Prometheus — GET /api/units/{id}/history (in-memory graph data) and GET /metrics (last-known values + scheduler counters, API-key gated, no live fetch).
• diag now checks the background service (running? enabled at boot? systemd/OpenRC/runit/procd/Windows).
• The web UI got scan-to-add too; the min-auth clamp now also refuses new v1 enrollment.

This asset: breeze-core-3.0.0.pre2-1.x86_64.rpm (self-contained, no Python). Smoke-tested: installs, runs, streams SSE, reports 3.0.0.pre2. Pairs with the Breeze app v2.0.0 prerelease 2 (SSE baked in). Built from overhaul @ 987911d. (CI attaches the full deb/rpm/apk/pacman/tarball matrix shortly.)