feat: add workspace-scoped private chats

[ibourgeois]

Summary

• add private workspace-scoped chat persistence with durable messages and participants
• wire active chat selection and message posting into the desktop shell
• keep chats private to their parent workspace and out of the shared workspace graph

Testing

• '/Users/ibourgeois/Library/Application Support/Herd/bin/php84' artisan test --compact tests/Feature/WorkspaceChatManagementTest.php tests/Feature/DesktopShellTest.php tests/Feature/InstanceConnectionManagementTest.php
• '/Users/ibourgeois/Library/Application Support/Herd/bin/php84' artisan test --compact tests/Feature/WorkspaceChatManagementTest.php tests/Feature/DesktopShellTest.php tests/Feature/DesktopUiFeatureFlagTest.php tests/Feature/WorkspaceManagementTest.php tests/Feature/SurrealSchemaDriverTest.php

Closes #134

[Copilot]

Pull request overview

Adds durable, workspace-scoped private chats (chats, participants, messages) and wires chat selection + message posting into the desktop shell while keeping this data out of the shared workspace graph.

Changes:

• Introduces workspace chat persistence (models, migrations, factories) including participants and durable messages.
• Adds chat/messaging controllers + form requests + routes, plus a WorkspaceChatManager and ViewerIdentityResolver.
• Updates the desktop shell (welcome view + tests) to show chats, activate chats, and post messages.

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Feature/WorkspaceChatManagementTest.php	New feature tests covering active chat resolution, chat creation/activation, and message posting.
tests/Feature/InstanceConnectionManagementTest.php	Extends connection UI assertions to include active chat content.
tests/Feature/DesktopShellTest.php	Updates shell expectations to reflect private chats + durable messages.
routes/web.php	Adds POST routes for creating chats, activating chats, and posting messages.
resources/views/welcome.blade.php	Switches shell from mock conversation UI to real workspace chat rendering + forms.
database/migrations/2026_03_27_143427_add_active_chat_id_to_connection_workspaces_table.php	Adds active_chat_id to workspaces (FK for SQL, numeric for Surreal).
database/migrations/2026_03_27_143418_create_workspace_chats_table.php	Creates workspace_chats table with workspace scope + slug uniqueness (SQL).
database/migrations/2026_03_27_143418_create_workspace_chat_participants_table.php	Creates participants table with optional user_id + uniqueness (SQL).
database/migrations/2026_03_27_143418_create_workspace_chat_messages_table.php	Creates durable messages table scoped to a chat.
database/factories/WorkspaceChatFactory.php	Factory for workspace chats (group/direct).
database/factories/WorkspaceChatParticipantFactory.php	Factory for chat participants (human/agent).
database/factories/WorkspaceChatMessageFactory.php	Factory for chat messages.
app/Support/Connections/ViewerIdentityResolver.php	Extracts viewer identity derivation from connection/session context.
app/Support/Chats/WorkspaceChatManager.php	Centralizes chat list/active chat creation, chat creation, activation, and message creation.
app/Models/WorkspaceChat.php	New chat model + workspace/participants/messages relationships.
app/Models/WorkspaceChatParticipant.php	New participant model + chat/user relationships.
app/Models/WorkspaceChatMessage.php	New message model + chat relationship.
app/Models/Workspace.php	Adds active_chat_id, activeChat() and chats() relationships.
app/Http/Requests/StoreWorkspaceChatRequest.php	Validates chat creation input.
app/Http/Requests/StoreWorkspaceChatMessageRequest.php	Validates message posting input.
app/Http/Controllers/HomeController.php	Wires chat state into the shell view (active chat, links, participants, messages).
app/Http/Controllers/ChatController.php	Handles chat creation + activation from the shell.
app/Http/Controllers/ChatMessageController.php	Handles message posting into a workspace chat.

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