feat(workflow): key/value editor for headers & query params

[simlarsen]

Kills the biggest remaining raw-JSON footgun: HTTP headers / query params. Stacked on #2610.

What

StringDictionary arguments (headers and query params on the API & Webhook components) were hand-written JSON — a {"Authorization": "Bearer x"} blob that's easy to get wrong. They're now edited as key/value rows: add, remove, type a name and a value.

• Pure KeyValueUtils (parseKeyValue / serializeKeyValue): the value stays a JSON string on disk, so the server parses it to the same object and execution is unchanged. Values keep any {{ tokens }} verbatim.
• KeyValueInput renders the rows, with an "Edit as JSON" escape — and it starts in JSON mode automatically when the value is nested/invalid, so nothing strands the user.
• ArgumentsForm routes StringDictionary to it (removed from the JSON-editor set) and suppresses the data-reference footer for it, since editing is inline.

Verification

• KeyValueUtils.test.ts: flat object → rows; token-in-value preserved; scalar coercion; array / nested / invalid → null (→ JSON fallback); empty → []; serialize drops empty-key rows, empty → "", and round-trips to the same parsed object.
• KeyValueInput.test.tsx (RTL): renders a row per pair, serializes edits back to a JSON object, add/remove rows, and starts in JSON mode for nested values.
• 82 workflow tests pass; tsc ✓, eslint ✓.

🤖 Generated with Claude Code

[simlarsen]

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