Disclose frontend app and project workflow updates

[hoogvliets]

Part of the downstream AGPL disclosure. This PR isolates the frontend app and project workflow changes for easier review.

Scope

• Frontend-only source changes from the downstream codebase.
• Covers account, project, document, assistant, workflow, and tabular review UI changes.
• Full disclosure PR: Disclose downstream AGPL changes #127.

App Structure

• Moves shared providers, auth context, user profile context, logo, Supabase client, and utilities under frontend/src/app/.
• Adds ManifestsContext and useProjectHandlers for app-level project state and behavior.
• Updates imports after the app-tree consolidation.

Account Experience

• Updates account layout and model settings pages.
• Adds account deletion banner support.
• Connects frontend account flows to the backend account lifecycle changes.

Project and Document Workflows

• Reworks the project page into updated document, explorer, and workflow panels.
• Adds ProjectDocPanel, ProjectExplorerPanel, and shared PanelDivider.
• Updates document viewing, DOCX rendering, document modals, row actions, and side panel behavior.

Assistant, Workflow, and Tabular UI

• Updates assistant chat, model toggle, side panel, workflow modal, and initial view behavior.
• Updates tabular review panel and generation flows.
• Updates workflow list and workflow detail UI integration.

Package and Build Changes

• Updates frontend package dependencies and lockfiles.
• Keeps Next.js, React, OpenNext, Supabase, markdown, DOCX, and UI dependencies aligned with the downstream app.

Review Note

• This PR is intended as a reviewable frontend slice. It may depend on backend/database behavior disclosed in Disclose database migrations and Supabase config #130 and Disclose backend hardening and route changes #131 for full runtime functionality.