Support Gemma4/Tinfoil in Duck.ai model picker

[malmstein]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1174433894299346/task/1216112317576899
Tech Design URL (if applicable):

Description

The /models endpoint now returns Gemma4 (id: "tinfoil/gemma4-31b", provider: "Tinfoil"), an open-source model served by Tinfoil. The app had no mapping for it, so it resolved to UNKNOWN and rendered without an icon in the native input model picker.

This PR:

• Classifies Tinfoil-provided models as OSS, so Gemma4 reuses the existing ic_ai_model_oss_16 icon — matching what FE does.
• Matches on both the tinfoil/ id prefix and the provider string (mirroring how meta-llama / mistralai are detected), so classification survives a missing or renamed provider field.
• Normalises the provider string to lowercase, so backend capitalisation (e.g. "Tinfoil", "OpenAI") can no longer silently drop a model into UNKNOWN.
• Falls back to the OSS icon for UNKNOWN providers, so a model never renders without an icon again (per discussion on the iOS task — Windows already has a fallback).

Steps to test this PR

Gemma4 shows an icon in the model picker

• Build an internal flavour with the internal cookie so Gemma4 is returned by /models
• Open Duck.ai → native input → model picker
• Confirm Gemma4 appears with the OSS icon (same as GPT-OSS-120b), not blank

Unknown-provider fallback

• Confirm any model with an unrecognised provider shows the OSS icon rather than no icon

UI changes

Before	After
(Gemma4 with no icon)	(Gemma4 with OSS icon)

---

Note

Low Risk
UI-only provider classification and icon display in the Duck.ai model picker; no auth, networking, or chat routing changes.

Overview
Tinfoil / Gemma4 models from /models are now mapped to OSS in ModelProvider.from via tinfoil/ id prefix and provider: "tinfoil", aligned with FE. Provider strings are lowercased before matching so capitalized values (e.g. "Tinfoil", "OpenAI") no longer misclassify as UNKNOWN.

The native model picker always shows a leading icon: getIconResForModel returns a non-null drawable and UNKNOWN uses the same ic_ai_model_oss_16 fallback as OSS. ModelPickerView.setLeadingIcon is simplified to require a drawable resource instead of optional icons.

^{Reviewed by Cursor Bugbot for commit 1a24247. Bugbot is set up for automated code reviews on this repo. Configure here.}