Create REST request flow (all HTTP methods, body, headers) — CLI & TUI

[syncended]

Goal

Support the full flow of authoring a REST request and sending it. Must work in both interfaces:

• CLI — non-interactive command(s) for scripting / one-shot use
• TUI — interactive screens for building a request step by step

Scope

• All standard HTTP methods: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS
• Request URL (with path / query parameters)
• Headers (add / edit / remove, multi-value)
• Body:
  • raw (text / JSON)
  • form-urlencoded
  • multipart/form-data (incl. file uploads)
• Sending the request and displaying the response (status, headers, body)

Out of scope (separate issues)

• Saved/named requests, collections, environments
• Auth helpers (Bearer, Basic, OAuth)
• Scripting / pre-request hooks
• TUI main screen layout — tracked in its own issue

Acceptance criteria

• A user can compose and send a request with any of the listed methods from the CLI.
• A user can compose and send the same request interactively in the TUI.
• Both interfaces share the underlying request model / executor (no duplicated logic).

[syncended]

Decisions (roadmap planning, 2026-04-27)

• HTTP client: Ktor client (Kotlin-native, coroutines already in deps).
• Architecture: shared logic lives in a new `:core` module — request/response domain model and `RequestExecutor`. Tracked in Set up :core module with Ktor client and base request/response model #10.
• Body types in scope: raw, JSON, form-urlencoded, multipart (incl. file uploads).
• Saved-requests format: `.http` (IntelliJ/VSCode REST Client conventions) — tracked in Saved requests on disk: .http format, 1 file = 1 request, dirs as groups #11.

This issue covers the CLI and TUI surface on top of `:core`. TUI surface coordinates with #5.