chore: bubbletea v2 migration

[theantichris]

No description provided.

[Copilot]

Pull request overview

This PR migrates the codebase from bubbletea v2 release candidate versions to the stable v2.0.0 release. The migration involves updating API usage to match breaking changes in the stable release, specifically around keyboard event handling and view rendering.

Changes:

• Updated keyboard event handling from tea.KeyMsg to tea.KeyPressMsg across all UI components
• Changed View content validation from nil check to empty string check in tests
• Updated dependencies from RC versions to stable v2.0.0 releases for bubbletea, bubbles, and lipgloss

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/ui/thread_list_test.go	Updated test to check for empty string instead of nil for View content
internal/ui/stream.go	Changed case statement from tea.KeyMsg to tea.KeyPressMsg
internal/ui/chat_normal.go	Updated function signature to accept tea.KeyPressMsg
internal/ui/chat_insert.go	Updated function signature to accept tea.KeyPressMsg
internal/ui/chat_command.go	Updated function signature to accept tea.KeyPressMsg
internal/ui/chat.go	Updated case statements and function signatures to use tea.KeyPressMsg
go.mod	Updated main dependencies from RC to stable v2.0.0 versions, updated transitive dependencies
go.sum	Updated checksums for all updated dependencies

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