[UI]: Simplification & hygiene plan (requests, stores, deps)

[misi-bp]

Problem Statement

• Standardize all frontend HTTP on native fetch via a shared HTTP client layer (fetchJson, fetchNdjsonStream, fetchSse).
• Today the UI mixes axios (4 files) and fetch (9+ call sites) with divergent error parsing.
• Three Zustand streaming stores duplicate connect/parse/abort logic.
• TypeScript API types are hand-written and drift from the OpenAPI spec.
• Dependency hygiene: remove unused @reactflow/node-resizer and axios; declare zustand explicitly.

Priorities: dependency fix → fetch HTTP layer → migrate all call sites → streaming store factory → OpenAPI codegen.

Proposed Solution

1. Dependency hygiene
2. HTTP client layer: httpFetch + fetchJson + fetchNdjsonStream + fetchSse
3. Migrate all call sites off axios and raw fetch
4. Streaming store factory on fetchNdjsonStream
5. Check why and how OpenAPI types are used. Assess if we can use TS codegen for generating them.
6. URL/env documentation + optional single base

Alternatives Considered

No response

Additional Context

No response

Checklist

• I have read the contributing guidelines
• I have verified this does not duplicate an existing feature request