fix(credits): suppress usage gauge when top-up funds exist + add display.credits_notices toggle (#44716)

The subscription-cap usage gauge (50/75/90% bands) ignored purchased
(top-up) credits: a sub user with top-up funds got a sticky warn banner
at 90% of their cap — permanently at >=100%, alongside grant_spent —
despite being fully able to keep inferencing. The cap is the wrong
denominator for an account that can keep spending.

- evaluate_credits_notices: purchased_micros > 0 suppresses the usage
  band (grant_spent already covers the cap-reached + top-up case with
  the remaining balance). A top-up landing mid-session clears any
  showing band; spending top-up down to 0 resumes the gauge.
- New display.credits_notices config (default true): false silences all
  credits notices. State capture and /usage are unaffected. Read once
  per agent (cached) in _emit_credits_notices, fail-open true.
- Docs: configuration.md display block.

hermes_cli/config.py

@@ -1438,6 +1438,11 @@ DEFAULT_CONFIG = {
         # class of over-claim that otherwise forces users to run
         # `git status` to verify edits landed.  Set false to suppress.
         "file_mutation_verifier": True,
+        # Nous credits status-bar notices (usage bands, grant-spent, depleted /
+        # restored).  When false, no credits notices are emitted — balance data
+        # is still captured and /usage keeps working.  Off switch for sub +
+        # top-up users who find the gauge noisy.
+        "credits_notices": True,
         # Turn-completion explainer.  When true (default), the agent appends a
         # one-line explanation to its final response whenever a turn ends
         # abnormally with no usable reply — empty content after retries, a