fix: make registry components self-contained with ConversationProvider (#77)

* revert: remove RegistryPreviewProvider wrapper from registry views

Reverts the approach of wrapping registry previews in a shared
ConversationProvider. Components will instead be made self-contained.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: make registry components self-contained with ConversationProvider

Each voice-chat page and the conversation-bar demo now wraps itself
with ConversationProvider instead of relying on an external wrapper.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: export PageContent so frontpage shares a single ConversationProvider

The frontpage CardsDemo imports PageContent (without provider) so all
voice-chat blocks share one ConversationProvider. The default Page
export keeps its own provider for standalone/registry use.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* chore: regenerate registry JSON files

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: rename PageContent to block-specific names (VoiceChat01/02/03)

Makes the named exports self-descriptive, removing the need for import
aliases when consuming the unwrapped components.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>