feat(desktop): show model pricing + free/paid tier gating in GUI picker

The CLI `hermes model` picker shows per-model $/Mtok pricing and gates paid
models on free Nous accounts. The GUI picker showed bare model names. Bring it
to parity across both the model-picker dialog and onboarding confirm card.

Backend:
- inventory.build_models_payload gains a pricing=True flag → _apply_pricing
  enriches each provider row with formatted per-model pricing
  ({input,output,cache,free}) via the same _format_price_per_mtok the CLI uses,
  and for Nous adds free_tier + unavailable_models (paid models a free user
  can't select) via check_nous_free_tier + partition_nous_models_by_tier.
  Best-effort: any pricing/tier failure is swallowed and fails open (no gating).
- /api/model/options and TUI model.options now pass pricing=True so the
  global picker and in-session picker both carry pricing.

Frontend:
- ModelOptionProvider gains pricing/free_tier/unavailable_models; new
  ModelPricing type.
- model-picker dialog renders In/Out $/Mtok (or a Free pill) per model, a
  Free tier/Pro badge on the Nous heading, and disables + grays unavailable
  paid models for free users with a 'Pro models need a paid subscription' note.
- onboarding confirm card shows the chosen model's price + tier badge.

Tests: test_inventory_pricing covers price formatting, free-tier gating,
paid no-gating, providers without pricing, and swallowed failures.

hermes_cli/inventory.py

@@ -114,6 +114,7 @@ def build_models_payload(
     include_unconfigured: bool = False,
     picker_hints: bool = False,
     canonical_order: bool = False,
+    pricing: bool = False,
     max_models: int = 50,
 ) -> dict:
     """Build the ``{providers, model, provider}`` shape every consumer
@@ -128,6 +129,11 @@ def build_models_payload(
     - ``canonical_order``: reorder canonical-slug rows to
       ``CANONICAL_PROVIDERS`` declaration order; truly-custom rows go
       last (TUI display order).
+    - ``pricing``: enrich each row with formatted per-model pricing and,
+      for Nous, ``free_tier``/``unavailable_models`` so the GUI picker can
+      show $/Mtok columns and gate paid models on free accounts —
+      mirroring the ``hermes model`` CLI picker. Adds network calls
+      (pricing fetch + Nous tier check); only set for interactive pickers.
     """
     from hermes_cli.model_switch import list_authenticated_providers
 
@@ -146,6 +152,8 @@ def build_models_payload(
         _apply_picker_hints(rows)
     if canonical_order:
         rows = _reorder_canonical(rows)
+    if pricing:
+        _apply_pricing(rows)
 
     return {
         "providers": rows,
@@ -238,3 +246,85 @@ def _reorder_canonical(rows: list[dict]) -> list[dict]:
     )
     extras = [r for r in rows if r["slug"] not in order]
     return canon + extras
+
+
+def _apply_pricing(rows: list[dict]) -> None:
+    """Enrich each provider row with per-model pricing + Nous tier gating.
+
+    Mutates ``rows`` in-place. For every row whose provider supports live
+    pricing (openrouter / nous / novita) adds::
+
+        row["pricing"] = {model_id: {"input": "$3.00", "output": "$15.00",
+                                     "cache": "$0.30" | None, "free": bool}}
+
+    For Nous additionally adds::
+
+        row["free_tier"] = bool            # current account is free-tier
+        row["unavailable_models"] = [...]  # paid models a free user can't pick
+
+    Prices are pre-formatted via ``_format_price_per_mtok`` so the GUI just
+    renders strings — identical formatting to the CLI picker. All failures
+    are swallowed (best-effort): a row simply gets no ``pricing`` key.
+    """
+    from hermes_cli.models import (
+        _format_price_per_mtok,
+        check_nous_free_tier,
+        get_pricing_for_provider,
+        partition_nous_models_by_tier,
+    )
+
+    # Resolve Nous free-tier once (cached in models.py for the TTL window).
+    nous_free_tier: Optional[bool] = None
+
+    for row in rows:
+        slug = str(row.get("slug", "")).lower()
+        models = row.get("models") or []
+        if not models:
+            continue
+        try:
+            raw_pricing = get_pricing_for_provider(slug) or {}
+        except Exception:
+            raw_pricing = {}
+        if not raw_pricing:
+            continue
+
+        formatted: dict[str, dict] = {}
+        for mid in models:
+            p = raw_pricing.get(mid)
+            if not p:
+                continue
+            inp_raw = p.get("prompt", "")
+            out_raw = p.get("completion", "")
+            cache_raw = p.get("input_cache_read", "")
+            inp = _format_price_per_mtok(inp_raw) if inp_raw != "" else ""
+            out = _format_price_per_mtok(out_raw) if out_raw != "" else ""
+            cache = _format_price_per_mtok(cache_raw) if cache_raw else None
+            # A model is "free" when both input and output cost nothing.
+            is_free = inp == "free" and (out == "free" or out == "")
+            formatted[mid] = {
+                "input": inp,
+                "output": out,
+                "cache": cache,
+                "free": is_free,
+            }
+
+        if formatted:
+            row["pricing"] = formatted
+
+        if slug == "nous":
+            try:
+                if nous_free_tier is None:
+                    nous_free_tier = check_nous_free_tier(force_fresh=True)
+                row["free_tier"] = bool(nous_free_tier)
+                if nous_free_tier:
+                    _selectable, unavailable = partition_nous_models_by_tier(
+                        list(models), raw_pricing, free_tier=True
+                    )
+                    row["unavailable_models"] = unavailable
+                else:
+                    row["unavailable_models"] = []
+            except Exception:
+                # Tier detection failed — fail open (no gating) so the user
+                # is never blocked from picking a model.
+                row["free_tier"] = False
+                row["unavailable_models"] = []

hermes_cli/web_server.py

@@ -1311,7 +1311,7 @@ def get_model_options():
     try:
         from hermes_cli.inventory import build_models_payload, load_picker_context
 
-        return build_models_payload(load_picker_context(), max_models=50)
+        return build_models_payload(load_picker_context(), max_models=50, pricing=True)
     except Exception:
         _log.exception("GET /api/model/options failed")
         raise HTTPException(status_code=500, detail="Failed to list model options")