[codex] Add MCP-backed graph dashboard auth flow

[elysemukamisha]

What changed

• added an MCP-backed graph experience to the Next dashboard, including graph routes, search, and the Graph explorer UI
• rewired dashboard data access away from the missing open-brain-rest function and onto the deployed MCP-backed endpoints
• replaced direct MCP-key login with Supabase Auth plumbing, including email/password plus Google and GitHub OAuth entry points and the auth callback flow
• updated dashboard pages that depended on the old REST API so thoughts and related views work in MCP mode

Why

The deployed project does not expose the REST function this dashboard was originally built against, which caused 404 failures across login, dashboard, and thoughts flows. This PR moves the dashboard onto the backend that actually exists and adds the graph view the project wanted.

Impact

• dashboard and thoughts load against the live MCP-backed backend instead of failing on missing REST endpoints
• graph view is available in the sidebar and thought flow
• login UI supports Supabase Auth-based sign-in flows instead of asking end users for the MCP access key

Validation

• npm run lint
• npx tsc --noEmit
• verified local and deployed dashboard routes during implementation

Notes

• GitHub and Google OAuth still require those providers to be enabled in the Supabase project before the social buttons can complete sign-in

[github-actions]

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