ui: Batch/Transaction workspace — upload, preflight review, execute, results summary

[angela-helios]

From the review call on Brett's Batch/Transaction designs, updated 2026-07-31 against the new Figma frames (330:461 Upload, 330:2 Actions, 330:720 Bundle JSON, 330:1141 Response) — the designs cover the agreed flow; this issue is the implementation.

Flow (per the frames)

1. Upload — drop/browse a Bundle JSON file.
2. Preflight (Actions) — request line (POST [base] · Bundle·{type}·{n} entries), one row per entry with its HTTP method chip and target URL, collapsible body per row (chevrons in the design), Bundle JSON tab with the raw payload, Cancel / Upload another / Execute. Entry methods are display-only.
3. Execute — POST to the server root.
4. Response — per-action outcomes with the status badges, Execute again / Back to bundle.

Implementation requirements beyond the mock

• Aggregate result summary (Steve, not in the mock): the Response page states how many resources were created / updated / failed, not just per-row badges.
• Batch-vs-transaction explainer: one line of copy in the preflight stating the semantics of what is about to run — transaction: all-or-nothing; batch: independent entries, failures don't stop the rest.
• Texts come from the real payload, not the mock: the bundle type shown is the uploaded bundle's type (the mock mixes batch in the header with transaction in the JSON), and per-entry statuses render verbatim from the response bundle (201 Created, not the mock's 200 CREATED). Flagged to Brett as example-text nits; implementation is the source of truth.
• GET entries are in-scope: per the R4 spec, transaction processing explicitly includes "Process any GET or HEAD interactions" (step 4), and the server already supports them (BundleMethod::Get).

Out of scope (decided 2026-07-31)

• Single-resource upload path and a dedicated expanded-accordion mock (Edson's suggestions — dropped).
• Import ($bulk-submit) and Export remain separate nav entries and separate work.