Delete DuckChatWebViewActivity

[joshliebe]

Task/Issue URL: https://app.asana.com/1/137249556945/project/488551667048375/task/1211755763011422?focus=true

Description

• This is no longer needed since Duck.ai is currently tied to the BrowserActivity using DuckChatWebViewFragment

Steps to test this PR

• Open Duck.ai
• Verify that it is launched correctly

---

Note

Deletes the standalone DuckChatWebViewActivity and shifts opening/closing Duck.ai to BrowserNav with updated session handling; cleans up manifest and tests.

• DuckChat flow:
  • Remove DuckChatWebViewActivity and DuckChatWebViewActivityViewModel (and related tests).
  • In RealDuckChat, drop keepSession and standalone activity path; always use BrowserNav.openDuckChat/closeDuckChat.
  • Adjust session logic: hasSessionActive now based on hasActiveSession() unless forceNewSession.
  • Remove DuckChatWebViewActivityWithParams usage and startDuckChatActivity helper.
• Manifest:
  • Delete com.duckduckgo.duckchat.impl.ui.DuckChatWebViewActivity entry.
• Tests:
  • Update RealDuckChatTest to assert BrowserNav intents and active-session behavior; remove obsolete WebView activity tests.

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[joshliebe]

• Delete DuckChatWebViewActivity #7328 👈 (View in Graphite)
• develop

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[malmstein]

Nice clean up 🔥

Some tests are failing but I’m approving so it’s not blocked