fix(server): keep cost throttles on for positive fractional limits

A limit such as 0.5 floored to 0 and disabled the throttle, although only an
explicit 0 is meant to. Positive values below 1 now count as 1.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.env.example

@@ -40,7 +40,7 @@ GOOGLE_MAPS_SERVER_API_KEY=
 # with a positive integer; 60 is a sensible tightening whenever HOST is not
 # localhost. Set it to exactly 0 to run unthrottled. An unreadable value (a
 # typo, a stray unit) falls back to the default rather than to unlimited, so a
-# slip cannot quietly disarm the guard.
+# slip cannot quietly disarm the guard. A positive value below 1 counts as 1.
 # NOTE: this is a per-IP, process-local guard (in-memory, resets on restart;
 # over-limit requests get a sanitized 429) — it is NOT a billing cap. For hard
 # spend protection set provider-side budget alerts: Google Cloud Console ->
@@ -75,7 +75,7 @@ OPENAI_HUD_SUMMARY_MODEL=gpt-5-nano
 # and a voice session mints one token. Raise or lower it with a positive
 # integer; set it to exactly 0 to run unthrottled. An unreadable value (a typo,
 # a stray unit) falls back to the default rather than to unlimited, so a slip
-# cannot quietly disarm the guard.
+# cannot quietly disarm the guard. A positive value below 1 counts as 1.
 # NOTE: this is a per-IP, process-local guard (in-memory, resets on restart;
 # over-limit requests get a sanitized 429) — it is NOT a billing cap. For hard
 # spend protection set a provider-side budget: OpenAI platform -> Settings ->