Extend retry backoff; rework logging (LOGLEVEL, request lines, colors)

Backoff now covers all dial-phase errors (refused, timeout, DNS), TLS
handshake failures, and 5xx responses with replayable bodies; streamed
POSTs are never replayed to avoid duplicate work. First retry of an
episode logs at WARN, subsequent attempts at INFO.

LOGLEVEL (LOG_LEVEL kept as alias) now defaults to warn: startup logs
version plus every setting; INFO adds one line per incoming request and
per response with status/duration, ANSI-colored in text mode (bypasses
slog's escaping so colors render in docker compose logs); NO_COLOR or
LOG_FORMAT=json disables colors.

README.md

@@ -41,7 +41,7 @@ startup.
 | `JOB_TIMEOUT` | `15m` | Wait for a ComfyUI job to finish |
 | `LLM_WAIT_TIMEOUT` | `10m` | Max lock wait for an LLM request before 503 |
 | `WARM_MODEL` | _(empty)_ | Model to reload after an image job (off by default) |
-| `LOG_LEVEL` | `info` | `debug` logs every lock transition |
+| `LOGLEVEL` | `warn` | `info` logs every request (colored arrows in text mode), `debug` adds lock transitions. `LOG_LEVEL` works as an alias |
 | `LOG_FORMAT` | `text` | `json` for structured JSON logs |
 | `UNLOAD_POLL_INTERVAL` | `500ms` | `/api/ps` poll interval while unloading |
 | `HISTORY_POLL_INTERVAL` | `1s` | `/history/<id>` poll interval while a job runs |
@@ -60,6 +60,12 @@ startup.
   `gpu_turnstile_llm_inflight`, `gpu_turnstile_image_pending`,
   `gpu_turnstile_image_jobs_total`, `gpu_turnstile_lock_wait_seconds`
   (histogram, `kind="llm|image"`), `gpu_turnstile_unload_seconds`.
+- Logs: startup logs the version and every setting (visible even at the
+  default `warn` level). With `LOGLEVEL=info` or `debug`, every request
+  logs a `-->` incoming line and a `<--` response line with status and
+  duration — ANSI-colored (cyan incoming; green/yellow/red by status
+  class) in text mode, which renders in `docker compose logs` on Windows
+  Terminal. Set `NO_COLOR` to disable colors.
 
 ## Build and run