Disclose frontend app and project workflow updates

From the PR description

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: #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 #130 and #131 for full runtime functionality.