Survive transient dashboard errors instead of failing the run

Next's dev server intermittently answers a 500 while recompiling a route: it
reads a build manifest mid-write and cannot parse it. A single one of those
during the locate poll was fatal, so a blip in the pipeline killed a run partway
through an auth flow on Windows.

5xx responses and dropped connections are now a distinct TransientError, retried
until the step's own timeout. A 4xx still fails immediately — those are verdicts
about the request, not blips. If the errors persist all the way to the timeout,
the message says so rather than blaming a missing extension.

Error bodies are also summarised. A dev-server 500 replies with a full HTML page,
and printing it raw buried the one line that said what went wrong under kilobytes
of script tags.

This makes the client tolerant of the fault, which is not the same as fixing it:
the real answer on an automation host is to run a production build rather than
`next dev`, so those manifests are written once instead of continuously.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

clicker/runner.py

@@ -33,7 +33,7 @@ HEARTBEAT_SECONDS = 2.0
 # Bumped whenever the step vocabulary or the locate protocol changes. Reported in
 # the heartbeat so the dashboard can say "restart your runner" instead of letting
 # a stale process fail on a step type it has never heard of.
-VERSION = "0.12.0"
+VERSION = "0.13.0"
 
 # Shared with the heartbeat thread: whether a run is currently executing.
 _busy = threading.Event()