feat: interactive model picker for gateway (Discord/Telegram)

[Chukwuebuka-2003]

What does this PR do?

Adds an interactive model picker for the gateway that allows users to select a provider first, then a model from that provider. This addresses the issue where users with multiple providers need to know the exact provider:model-name string to switch models.

Related Issue

Fixes #3710

Type of Change

• ✨ New feature (non-breaking change that adds functionality)

Changes Made

• hermes_cli/model_picker.py — New shared picker logic with provider/model lists, favorites support via ~/.hermes/models.yaml, and formatting functions for all platforms
• hermes_cli/commands.py — Added /models command to the registry
• gateway/run.py — Added _handle_models_command() handler with conversation flow (provider → model → confirm) and state management
• gateway/platforms/discord.py — Added /models slash command and ModelPickerView class with button-based UI

How to Test

1. Run the gateway with Discord or Telegram enabled
2. Send /models to open the interactive picker
3. Select a provider (e.g., "2" for Anthropic)
4. Select a model from the list
5. Verify the model switches and confirmation shows

# Example conversation flow:
# User: /models
# Bot: Select provider:
#      1. OpenRouter (current)
#      2. Anthropic
#      ...
# User: 2
# Bot: Models for Anthropic:
#      1. claude-opus-4-6 ★ (favourite)
#      2. claude-sonnet-4-6
#      ...
# User: 1
# Bot: ✓ Switched to: claude-opus-4-6 via Anthropic
#      Previous: gpt-5.4 via openai-codex

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I've run pytest tests/ -q and all tests pass (671 passed in hermes_cli/)
• I've tested on my platform: macOS

Documentation & Housekeeping

• N/A — No documentation changes needed (existing /model docs apply)

[teknium1]

Thanks for the contribution @Chukwuebuka-2003! The core feature this PR implements — an interactive model picker for Discord and Telegram — was independently shipped to main in commit 5a2cf280a on 2026-04-06 (PR #5742), about a week after this PR was opened.

What's already on main:

• DiscordAdapter.send_model_picker() + ModelPickerView (embed + Select-menu two-step drill-down) — gateway/platforms/discord.py:2942
• Telegram inline-keyboard drill-down with provider → model navigation — gateway/platforms/telegram.py
• Capability-detection dispatch in GatewayRunner._handle_model_command() — gateway/run.py:5587
• Full switch logic: session override, agent cache evict, model note injection

The implementation on main integrates the picker into the existing /model command (bare /model with no args triggers the interactive picker) rather than adding a new /models command, which keeps the command surface clean.

Closing as implemented. Thanks again for the work here — the approach was sound and the timing just didn't line up. This is an automated hermes-sweeper review.

[alt-glitch]

Likely duplicate of #5742 — same interactive model picker feature, #5742 was merged.