Add basecamp files versions — HELD, blocked on the SDK

[jeremy]

Do not merge. Draft to preserve completed work and make the blocker visible.

Implements basecamp files versions <upload-id> over UploadsService.ListVersions, with the full completeness-bar treatment: command in files.go, catalog entry, API-COVERAGE.md row, skill mention, .surface, unit tests (endpoint reached, URL accepted, pagination contract), and smoke coverage including the vaults/docs alias leaves. bin/ci green.

Why it's held

The SDK method mistypes its response. A live read-only probe of GET /uploads/{id}/versions.json returns version events:

{ "id": 16850997498, "recording_id": 10165243019, "action": "active",
  "details": { "status_was": "drafted" }, "created_at": "…", "creator": { … } }

but ListUploadVersionsResponseContent is modeled as []Upload, so ListVersions decodes events into Upload structs. What this command actually prints today:

• title, filename, status, content_type, download_url — all blank, and blank as zero values, so nothing signals they're an artifact
• action, details, recording_id — dropped; the only fields saying what happened
• id is the event id, so it invites basecamp files show <id>, which 404s

Note that action here is active, not blob_changed — the endpoint returns the full event stream since publication, so file replacements are one subset of it, not the whole listing.

Blocked on

UploadsService.ListVersions returning an event type (ID, RecordingID, Action, Details, CreatedAt, Creator) rather than []Upload. The root cause is the OpenAPI description, so the fix likely belongs upstream of the generator with the hand-written service following. No issue is filed against basecamp-sdk yet — that's the next step for this to move.

The command itself is correct and ships as-is once the type is right.

Rebase note

This branch's API-COVERAGE.md row still claims full coverage for uploads. #621 corrects the summary to 183/184 and adds the ⚠️ blocked status. Rebase onto #621 before this lands, and flip the row back to ✅ at the same time.

(An earlier version of this description pointed at a COMMUNIQUE-sdk-upload-versions-response.md file in #621. That file was removed — basecamp-cli is public, and cross-team asks don't belong in its source tree. The content is preserved off-tree pending an SDK issue.)

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