feat(openai): cover gpt-5.6 -pro variants (PR #61587 complement)

PR #61587 adds sol-pro/terra-pro/luna-pro to the aggregator lists.
Complete those on the native surfaces the same way this PR completes
the base tiers:

- hermes_cli/models.py: -pro variants in _PROVIDER_MODELS[openai-api].
- agent/usage_pricing.py: alias ("openai", "gpt-5.6-*-pro") onto the
  base-tier PricingEntry rows — the -pro high-effort modes bill at the
  SAME per-token rates (verified against OpenRouter live pricing
  2026-07-09: identical prompt/completion prices for base and -pro);
  they cost more per task by consuming more tokens, not a higher rate.
- Context lengths need no new entries: "gpt-5.6-sol" et al. are
  substrings of their -pro variants and both lookup tables match
  longest-key-first (verified: sol-pro -> 1.05M direct / 272K codex).
- model_switch sort: -pro variants parse as suffix "sol-pro" (rank 1),
  so /model gpt still defaults to base sol — pinned by test.
- Not added to DEFAULT_CODEX_MODELS: only confirmed routable via API/
  OpenRouter so far; codex live discovery will surface them if ChatGPT
  exposes them, same policy as other unconfirmed codex slugs.

Tests: invariant tests extended (pro aliases share base entries, base
sol outranks sol-pro); 191 targeted tests pass.

hermes_cli/models.py

@@ -240,8 +240,11 @@ _PROVIDER_MODELS: dict[str, list[str]] = {
     ],
     "openai-api": [
         "gpt-5.6-sol",
+        "gpt-5.6-sol-pro",
         "gpt-5.6-terra",
+        "gpt-5.6-terra-pro",
         "gpt-5.6-luna",
+        "gpt-5.6-luna-pro",
         "gpt-5.5",
         "gpt-5.5-pro",
         "gpt-5.4",