fix: include Nous Portal free-tier models in /model picker

[pinguarmy]

Problem

The gateway /model picker (used in TUI and messaging platforms) doesn't show Nous Portal free-tier models like deepseek-v4-flash and stepfun/step-3.5-flash. Only the curated paid models appear.

The CLI hermes model command shows them correctly at the bottom under "Available free models", but the gateway picker omits them entirely.

Root Cause

list_authenticated_providers() in hermes_cli/model_switch.py loads the curated Nous model list from the remote catalog but never augments it with the Portal's freeRecommendedModels (or paidRecommendations for paid users).

The CLI hermes model (in hermes_cli/main.py) already handles this via:

• check_nous_free_tier() — detect user tier
• union_with_portal_free_recommendations() — add free models
• union_with_portal_paid_recommendations() — add paid models

But list_authenticated_providers() — which the gateway's /model command uses — doesn't call any of these.

Fix

Augment the Nous model list in list_authenticated_providers() with the Portal's recommended models, mirroring the CLI logic:

• Free-tier users: prepend freeRecommendedModels (so newly-launched free models show up even if the curated list is stale)
• Paid-tier users: prepend paidRecommendations

The augmentation is wrapped in a try/except so network failures or auth issues degrade gracefully to the curated list.

Testing

• All existing model_switch tests pass (71/71)
• 1 pre-existing failure (missing prompt_toolkit in test env, unrelated)

[alt-glitch]

Related to merged #24082 (Portal-flagged free models in picker) and open #26130 (add deepseek-v4-flash to curated list). This PR takes the approach of augmenting list_authenticated_providers() with the Portal recommended-models endpoint, similar to the existing CLI logic.

[pinguarmy]

Closing — this fix is already present in the current codebase. model_switch.py lines 1534-1548 import and use and for the Nous provider in the /model picker.