feature: add copy-as-code-snippet for requests on the Send page

[komen205]

What

Adds the ability to copy a request as a code snippet directly from the Send page, while editing it — without having to send it first and export from the View page.

A new copy button sits in the Send request line (between the URL input and the Send button). Clicking it opens a menu mirroring the View page's export context menu:

• "Copy as X Snippet" shortcut for the preferred format, when one is set
• A "Copy as Code Snippet" submenu with all available httpsnippet targets

Picking a format from the submenu copies the snippet and updates the persisted preferred format (uiStore.exportSnippetFormat), same as the View page behaviour.

How

• generateHarRequestFromRequestData() in har.ts builds an ExtendedHarRequest from not-yet-sent request data (decoded body, raw headers, HTTP/1.1), reusing the existing cookie parsing, postData generation, and non-UTF8 body fallback.
• generateCodeSnippetFromRequestInput() in export.ts feeds that through the same HAR-simplification + httpsnippet conversion as the existing View-page path, which was refactored into a shared helper so both stay in sync (content-length/content-encoding/H2 pseudo-header dropping etc).
• Snippet options are Pro-gated, matching the View page's export menu.
• Invalid in-progress URLs fail with an alert rather than copying a broken snippet, and the button is disabled while the URL is empty.

Tests

Added test/unit/model/ui/export.spec.ts covering snippet generation from request inputs: simple GET, POST with body (content-length dropped), content-encoding dropped with decoded body used, and a clear failure for invalid URLs. Full unit suite passes (894 tests).

🤖 Generated with Claude Code

[komen205]

Looks like this

CURL *hnd = curl_easy_init();

curl_easy_setopt(hnd, CURLOPT_CUSTOMREQUEST, "GET");
curl_easy_setopt(hnd, CURLOPT_URL, "http://android.httptoolkit.tech/config");

struct curl_slist *headers = NULL;
headers = curl_slist_append(headers, "Host: android.httptoolkit.tech");
headers = curl_slist_append(headers, "Connection: Keep-Alive");
headers = curl_slist_append(headers, "Accept-Encoding: gzip");
headers = curl_slist_append(headers, "User-Agent: okhttp/4.11.0");
curl_easy_setopt(hnd, CURLOPT_HTTPHEADER, headers);

curl_easy_setopt(hnd, CURLOPT_ACCEPT_ENCODING, "");

CURLcode ret = curl_easy_perform(hnd);

[komen205]

Not sure if this is worth to keep, the whole feature is already gated anyway.