Live page: streamed updates and a sliding chart

The server pushes each new step over server-sent events
(GET /api/v1/live/stream) the moment it is sampled, so updates no
longer arrive in uneven pairs. The chart slides left steadily between
steps instead of jumping, and the big numbers count to their new
value. Both stay still with reduced motion.

README.md

@@ -267,6 +267,7 @@ signed in: POST /auth/mfa/keys/begin · /auth/mfa/keys/finish?name= · PATCH|DEL
 signed in: POST /auth/mfa/recovery-codes
 GET    /status                           GET /stats?range=24h|7d|30d|90d
 GET    /live?since=                      (speed per peer, last 2 minutes in 2-second steps)
+GET    /live/stream                      (the same as server-sent events)
 GET    /server         PATCH /server     POST /server/rotate-key     GET /server/detect-ip
 GET    /peers          POST /peers       (returns the config and QR once)
 GET    /peers/{id}     PATCH /peers/{id} DELETE /peers/{id}
@@ -298,7 +299,9 @@ downloaded, `up` is what it uploaded.
 
 `GET /live` answers `{"step": 2, "size": 60, "points": [{"t": …, "peers":
 {"<id>": [down, up]}}]}` with speeds in bits per second, kept only in memory.
-With `since` (unix seconds) it returns only newer steps.
+With `since` (unix seconds) it returns only newer steps. `GET /live/stream`
+sends the same messages as server-sent events: the history first, then one
+message per new step.
 
 Latency is measured by pinging the peer's tunnel address every 30 seconds. Set
 it per peer with `PATCH /peers/{id}` `{"latencyCheck": "off"|"active"|"always"}`