feat: parse pasted curl commands in URL bar

[fprotimaru]

Summary

• Pasting a curl ... command into the URL bar auto-fills the active tab's method, URL, headers, and body.
• New src/utils/curl_parser.rs handles shell-style tokenizing (single/double quotes, backslash escapes, \<newline> continuations) and common flags: -X/--request, -H/--header, -d/--data*, -F/--form, -u/--user, -A/--user-agent, -e/--referer, -b/--cookie, --url, -G/--get, --location, -k/--insecure, etc.
• Body type is inferred (multipart from -F, JSON by content-type or shape, urlencoded if pairs, otherwise text). Method defaults to POST when data is present and -X is absent. JSON bodies are pretty-printed before being placed in the editor.
• After a successful paste, the URL input is replaced with just the parsed URL and the request view switches to the Body tab when a body is present.

Test plan

• cargo test (50 tests; 12 new curl-parser tests covering simple GET, explicit method, multiline JSON --data, urlencoded -d, multipart -F, basic auth, the real-world Veon prebid sample)
• Manual: paste the Veon curl into the URL bar — method=POST, URL set, Content-Type: application/json in headers, JSON body pretty-printed in Body tab
• Manual: paste a curl -F multipart command — multipart editor populates
• Manual: paste a curl with -u user:pass — Authorization: Basic ... added
• Manual: type a normal URL (no curl prefix) — no parsing kicks in

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