feat(frontend): SSR shells, account/models, AOAI-aware components

Pages and components that interact with the new auth + LLM boundaries.

  * Page components for the dynamic-segment routes are now SSR shells
    that delegate to client components reading the URL at runtime.
    Required by Next.js `output: "export"` - server-baked params
    resolve to the placeholder "_" regardless of the URL, so the
    runtime-shape lookup has to happen client-side.  Affects:
      - assistant/chat/[id]
      - projects/[id]
      - projects/[id]/assistant/chat/[chatId]
      - projects/[id]/tabular-reviews/[reviewId]
      - tabular-reviews/[id]
      - workflows/[id]
    Each gains a sibling *Client.tsx that holds the interactive logic.

  * Account → Models page                - surfaces OpenAI + Azure
                                           OpenAI alongside Anthropic /
                                           Google.  AOAI deployment
                                           dropdown queries
                                           /api/llm/azure-openai/deployments
                                           against the user's stored
                                           AOAI endpoint.

  * Account page                         - provider-aware header (entra
                                           hides supabase-only controls).

  * Assistant chat input + model toggle  - ApiKeyAvailability now
                                           includes openaiApiKey and
                                           azureOpenai availability so
                                           the model dropdown lights up
                                           the right options.

  * Tabular review components             - same boundary updates for
                                           the tabular chat panel.

  * /diagnostics/route/[id]              - dev-only client page that
                                           introspects how the static-
                                           export shell maps to the
                                           current URL; used while
                                           debugging the SSR shell
                                           pattern.

  * app/lib/modelAvailability.ts         - adds openaiApiKey +
                                           azureOpenai branches.

  * app/page.tsx                         - provider-aware redirect
                                           between supabase and entra
                                           login flows.