refactor: rename FlowChatScreen to FlowChatView

[divyanshub024]

Summary

FlowChatScreen is now FlowChatView. The widget was never a screen: it builds no Scaffold and no app bar, and its docs have always said to drop it in a scaffold body. With SidePanel and Modal on the roadmap it is the surface hosts will embed inside them, so the name now follows Flutter's convention for embeddable composites (TabBarView, PageView).

Everything the name touched moves with it:

• flow_chat_screen.dart is now flow_chat_view.dart, with the export and all doc comment cross references updated
• The docs page moves from components/chat-screen to components/chat-view, with a redirect from the old URL so existing links keep working
• README table and sample code, example app, and playground demos and snippets updated
• CHANGELOG gains a breaking entry under 0.2.0 (unreleased)
• The roadmap row is now "Chat View" in CLAUDE.md, AGENTS.md, and the docs roadmap

Prose that refers to the host's own screen (like the README's "Build a chat screen") is unchanged on purpose: the host builds the screen, flow_ui provides the view.

How this was verified

• flutter analyze clean in the package root, example/, and playground/
• dart format . produced no changes
• npm run build in docs/ passes, and the emitted redirect page at /components/chat-screen points to /components/chat-view
• Pure rename with no rendering change, so no visual pass beyond compiling the playground demos

Checklist

• flutter analyze lib and flutter analyze in example/ and playground/ are clean
• dart format . applied
• Exercised in the playground — with a stage demo added or updated if this is a new component or variant (not exercised: pure rename, nothing renders differently)
• No new entries under dependencies: in pubspec.yaml (Flutter SDK and flutter.dev packages only)
• Nothing model-facing — no prompts, schemas, or provider/network calls
• New public API is exported from lib/flow_ui.dart and documented in docs/ and the README table
• CHANGELOG.md updated for user-facing changes, with breaking changes called out
• PR title follows conventional commits (feat:, fix:, refactor:, docs:, chore:)

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Note

Medium Risk
Public API rename with no behavior change, but it is a breaking call-site update for every host using the chat surface.

Overview
Breaking rename: FlowChatScreen is now FlowChatView. The widget was never a screen (body-only, no Scaffold), and the name now matches Flutter’s embeddable-composite convention ahead of SidePanel/Modal.

The class, file (flow_chat_view.dart), barrel export, example, playground, README, and component docs all move with it. Docs live at /components/chat-view, with a redirect from /components/chat-screen. Constructor and behavior are unchanged — hosts only need to rename call sites.

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