fix(server): filter benign read-idle-reap WARN on streaming follows

[Sootopolis]

What

The server's idleTimeout installs a read-only Netty ReadTimeoutHandler (resets on inbound reads only). A job-log / progress follow (GET /api/jobs/{id}/{logs,progress}) is write-only server→client once the GET is sent, so the outbound JobLogStream keepalive can never reset that timer — every live follow is reaped on the 60s schedule, which zio-http logs as ZIO.logWarningCause("Fatal exception in Netty", Cause.die(ReadTimeoutException)). The follower already reconnects transparently (#161), so the reap is benign transport noise; the WARN spam (two per cycle since the progress stream landed in #166) was the only real damage.

This drops exactly that WARN at ProgressDisplay's ZLogger:

• Scoped — matches the exact zio-http message and a cause that is solely a ReadTimeoutException defect (no failure, no other defect), so an unrelated bare read-timeout WARN still logs.
• Fails open — a zio-http rename/wrap on upgrade just makes the (benign) WARN reappear rather than hiding any genuine fatal-Netty signal.
• Also fixes the stale CcasServer comment that claimed the keepalive resets the server read timer (it can't — writes don't reset a ReadTimeoutHandler).

Rejected alternatives: removing idleTimeout re-opens the indefinite dead-fd leak #158 closed (zio-http exposes no server SO_KEEPALIVE); blanket logWarningOnFatalError(false) would hide all fatal-Netty WARNs.

Fixes

Log-noise from the read-idle reaper vs. write-only streaming follows (surfaced after #166 doubled it). No linked issue — diagnosed in-session.

Testing

• TestProgressBar (+1 case): the reaper WARN is dropped; a different fatal-Netty WARN and a bare ReadTimeoutException under a different message both still log. testLoggerSwallowsThrow still passes (throwing thunk still caught).
• Full sbt test green via pre-push (1048 passed).
• Verified against zio-http v3.10.1 source: ServerInboundHandler.exceptionCaught logs Cause.die(t) with t = raw ReadTimeoutException.INSTANCE, then ctx.close() — exactly the shape the filter matches.

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https://claude.ai/code/session_015eWRWek8owPM5eDjatPVit