Remove duckAiPaidSettingsStatus feature toggle

[mikescamell]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1207908166761516/task/1212517664869201?focus=true

Description

Remove the duckAiPaidSettingsStatus feature toggle now that it has been confirmed stable. The toggle defaulted to TRUE and gated whether Duck.ai paid settings screens sync the status indicator with DuckChat enabled state and show branded icons.

• Remove toggle declaration from DuckChatFeature
• Simplify DuckAiPaidSettingsViewModel and DuckAiPlusSettingsViewModel — remove toggle checks, legacy code paths, and unused DispatcherProvider/DuckChatFeature dependencies
• Remove isDuckAiPaidSettingsFeatureEnabled from ViewState and simplify UI conditionals in DuckAiPaidSettingsActivity and DuckAiPlusSettingsView
• Update layout XML defaults to use branded icons (duckai_128, ic_duckduckgo_ai_color_24)
• Delete legacy drawable assets (duckai_ddg_128, ic_ai_chat_grayscale_color_24) and remove lint baseline entry
• Clean up tests — remove toggle-specific tests and simplify remaining ones

Steps to test this PR

Toggle removal

• Open Duck.ai paid settings screen — verify branded duckai_128 icon displays
• Verify status indicator syncs with DuckChat enabled/disabled state
• Verify "Enable in AI Features Settings" / "Manage in AI Features Settings" button text switches based on DuckChat state
• Open Pro/Premium settings — verify ic_duckduckgo_ai_color_24 icon shows for Duck.ai setting

UI changes

No visual changes — the "enabled" toggle path was already the default behavior.

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Note

Low Risk
Low risk removal of an always-on feature flag and dead code paths; main risk is unintended UI/state regression in Duck.ai paid settings screens due to simplified ViewModel wiring.

Overview
Removes the duckAiPaidSettingsStatus remote toggle and all associated branching logic, including ViewState fields and injected dependencies in the Duck.ai paid settings ViewModels.

The paid settings screens now always observe DuckChat enabled state and always render the branded Duck.ai icons; legacy drawables are deleted and the design-system lint baseline is updated accordingly. Tests are simplified by dropping toggle-specific setup and assertions.

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[catalinradoiu]

Tested and works as expected.