Update DuckChat.isEnabled to check config flag and user pref

[joshliebe]

Task/Issue URL: https://app.asana.com/1/137249556945/project/1200204095367872/task/1211088838900418?focus=true

Description

• Modifies DuckChat.isEnabled to check the config flag and user pref.

Steps to test this PR

Sanity check

• Disable Duck.ai user setting
• Verify that Duck.ai is disabled
• Enable Duck.ai user setting
• Verify that Duck.ai is enabled
• In feature flag inventory, disable aiChat feature flag
• Restart the app
• Verify that Duck.ai is disabled

[joshliebe]

• Update DuckChat.isEnabled to check config flag and user pref #6605 👈 (View in Graphite)
• develop

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[Copilot]

Pull Request Overview

This PR modifies the DuckChat feature to properly check both the config flag and user preference to determine if Duck.ai is enabled. Previously, the isEnabled() method only checked the remote config flag, but now it combines both the feature flag and user setting to make the determination.

Key changes:

• Updated DuckChat.isEnabled() to check both config flag and user preference
• Introduced isDuckChatFeatureEnabled() method to check only the config flag
• Updated URL detection logic to use the config flag check instead of the combined check

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
duckchat/duckchat-api/src/main/java/com/duckduckgo/duckchat/api/DuckChat.kt	Updated documentation to reflect that isEnabled() now checks both config flag and user preference
duckchat/duckchat-impl/src/main/java/com/duckduckgo/duckchat/impl/RealDuckChat.kt	Modified isEnabled() logic, added isDuckChatFeatureEnabled() method, and updated URL detection to use feature flag check
duckchat/duckchat-impl/src/main/java/com/duckduckgo/duckchat/impl/helper/DuckChatJSHelper.kt	Updated JS helper to use isDuckChatFeatureEnabled() instead of isEnabled() for handoff data
app/src/main/java/com/duckduckgo/app/browser/SpecialUrlDetector.kt	Simplified URL detection logic to rely on isDuckChatUrl() which now handles feature flag check internally
duckchat/duckchat-impl/src/test/kotlin/com/duckduckgo/duckchat/impl/RealDuckChatTest.kt	Added comprehensive test coverage for all combinations of feature flag and user preference states
duckchat/duckchat-impl/src/test/kotlin/com/duckduckgo/duckchat/impl/helper/RealDuckChatJSHelperTest.kt	Updated test mocks to use isDuckChatFeatureEnabled() instead of isEnabled()
app/src/test/java/com/duckduckgo/app/browser/SpecialUrlDetectorImplTest.kt	Simplified tests to rely on isDuckChatUrl() handling feature enablement internally