Refuse a script/loadtest clients count that starts with 0

vegeta reads a leading 0 in its worker count as octal, so 00 gave no
workers and 010 gave eight. The clients check before the build now
refuses any value starting with 0, zero included. The duration needs no
change: vegeta reads it as decimal, so 05s is five seconds.

TODO.md: the load test entry is once, at the top of Completed Steps,
and the entries for #206 and
#204 are no longer repeated.

Model: opus-5-5

TODO.md

@@ -31,27 +31,6 @@ P2: security: per-IP rate limiting on the image routes
 
 # Completed Steps
 
-- 2026-10-04 `config.yml` stays out of git and the Docker build context (closes
-  #212): `.gitignore` now ignores `config.yml`, the config file Getting Started
-  creates with the signing key, and `.dockerignore` leaves it out in every
-  directory and in any letter case, as it already did `config.yaml` and
-  `config.dev.yml`.
-- 2026-10-04 local config files stay out of the Docker build context (closes
-  #211): `.dockerignore` now leaves out `config.yaml` and `config.dev.yml` in
-  every directory and in any letter case, the local config files `.gitignore`
-  keeps out of git because they can hold the signing key.
-  `configs/config.example.yml` is still sent. `config.yml`, which Getting
-  Started creates, is in neither file:
-  https://git.eeqj.de/sneak/pixa/issues/212.
-- 2026-10-04 `cmd/pixad/main.go` is one call into `internal/` (closes #206):
-  what it did (the command line and its `--config` flag, setting
-  `PIXA_CONFIG_PATH`, ignoring `SIGPIPE`, starting the fx app) is now `Run` in
-  `internal/app`, unchanged, and `main` calls it with `Version`, which the build
-  still sets through `-X main.Version`. That code had no tests to move.
-- 2026-10-04 `.gitignore` ignores `.claude/` (closes #204): the entry and its
-  comment are copied from the canonical `.gitignore` in `sneak/prompts`,
-  unanchored so it matches at every depth. `.dockerignore` already has
-  `.claude`.
 - 2026-10-04 load test (closes #81): `script/loadtest [duration [clients]]`
   (`make loadtest`, defaults `10s` and `4`), a benchmark that `script/check`
   does not run, measures three scenarios, each against a new pixad container and
@@ -67,6 +46,18 @@ P2: security: per-IP rate limiting on the image routes
   not pixad's limit); `miss` 70 r/s, p50 52 ms, p95 91 ms, p99 122 ms, peak 100
   MiB, one fetch per request; `herd` 74 r/s, p50 52 ms, p95 69 ms, p99 111 ms,
   peak 60 MiB, 188 fetches for 749 requests.
+- 2026-10-04 `config.yml` stays out of git and the Docker build context (closes
+  #212): `.gitignore` now ignores `config.yml`, the config file Getting Started
+  creates with the signing key, and `.dockerignore` leaves it out in every
+  directory and in any letter case, as it already did `config.yaml` and
+  `config.dev.yml`.
+- 2026-10-04 local config files stay out of the Docker build context (closes
+  #211): `.dockerignore` now leaves out `config.yaml` and `config.dev.yml` in
+  every directory and in any letter case, the local config files `.gitignore`
+  keeps out of git because they can hold the signing key.
+  `configs/config.example.yml` is still sent. `config.yml`, which Getting
+  Started creates, is in neither file:
+  https://git.eeqj.de/sneak/pixa/issues/212.
 - 2026-10-04 `cmd/pixad/main.go` is one call into `internal/` (closes #206):
   what it did (the command line and its `--config` flag, setting
   `PIXA_CONFIG_PATH`, ignoring `SIGPIPE`, starting the fx app) is now `Run` in