Add reasoningMode and getChatById to DuckAiChat Store

[YoussefKeyrouz]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1212810093780571/task/1215002056518125?focus=true

Description

Per-chat reasoning persistence groundwork (1 of 3).

The FE has been storing a reasoningMode field per chat in the JSON blob it pushes to native storage, but Android wasn't reading it. This PR starts extracting that field on the read side so it's available to consumers, and adds a single-chat lookup API to the store. No behavioural change yet - the new field isn't consumed by any feature in this PR.

The follow-up PR will use this data to populate the reasoning picker correctly when the user opens an existing chat (showing the chat's stored mode rather than the global default).

What changed:

• DuckAiChat Added a nullable reasoningMode: String? field.
• **New API: getChatById** on DuckAiChatStore. Wraps the existing chatsDao.getById(chatId)`.

No migration required. Room only stores (chatId, data) where data is the raw FE blob, we just parse a new field at read time.

Steps to test this PR

• Submit a duck.ai chat after selecting a model and reasoning effort (e.g. gpt 5 mini - fast)
• Go to Settings -> Duck.ai in developer settings -> Enable Native Storage Debug
• Validate that the chat is now stored with the selected “reasoningMode"

UI changes

N/A — data-layer only.

---

Note

Low Risk
Low risk data-layer change that only extends the parsed chat metadata and adds a read-only lookup API; main risk is minor integration/consumer expectations around null/empty reasoningMode handling.

Overview
Adds per-chat reasoningMode: String? to DuckAiChat and updates JSON parsing to populate it while treating missing, empty, or explicit JSON null as null.

Extends DuckAiChatStore with getChatById(chatId) (implemented in RealDuckAiChatStore) to fetch and parse a single chat, and adds unit tests covering reasoningMode parsing and the new lookup behavior (not found / malformed JSON).

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[YoussefKeyrouz]

• Add reasoningMode and getChatById to DuckAiChat Store #8659 👈 (View in Graphite)
• Upsell ai reasoning effort #8648
• Add reasoning effort access to the AI chat model #8625
• develop

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[malmstein]

Nice work!