Use backend podcast estimates and remove frontend cost heuristics

[AJaySi]

Motivation

• Remove fragile client-side heuristics that duplicated pricing logic and could diverge from real provider costs.
• Centralize estimate computation in the backend so the UI shows server-provided totals and per-phase breakdowns based on the current pricing catalog.
• Ensure the frontend displays only backend-provided estimates and shows a clear “Unavailable” fallback when the server does not supply an estimate.

Description

• Removed the local heuristic estimator from CreateModal.tsx and stopped injecting inferred constants into the create UI by passing estimatedCost={null} into the topic input component.
• Updated TopicUrlInput.tsx to accept a nullable estimatedCost and render an explicit Est. Unavailable chip when no server estimate is present.
• Removed the frontend estimateCosts heuristic and now map the backend analysisResp.data.estimate into the frontend CreateProjectResult.estimate (nullable) in frontend/src/services/podcastApi.ts.
• Extended the frontend PodcastEstimate typing to include backend metadata (breakdown, currency, lastUpdated) and allowed CreateProjectResult.estimate to be null in frontend/src/components/PodcastMaker/types.ts.
• Added server-side estimate generation in the podcast analysis handler (backend/api/podcast/handlers/analysis.py) that reads pricing catalog entries (cost_per_input_token, cost_per_output_token, cost_per_request, etc.) via PricingService, applies phase-level usage assumptions for Analyze/Gather/Write/Produce, and returns a user-facing estimate payload.
• Added the estimate field to the API response model PodcastAnalyzeResponse (backend/api/podcast/models.py) so the frontend receives precomputed totals and a phase breakdown.

Testing

• Ran Python syntax checks with python -m py_compile backend/api/podcast/handlers/analysis.py backend/api/podcast/models.py, which completed successfully.
• Attempted frontend type validation with npm --prefix frontend run -s typecheck and npm --prefix frontend exec tsc -- --noEmit, but tsc invocation failed in this environment due to npm registry policy (403) and could not complete here.
• No runtime regressions were observed in server-side compilation steps in this environment after the changes.

---

Codex Task