feat(attach): list the images one folder down, for the camera layout

[ewanc26]

What this changes

wf_attach_scan_images_tree: the images in a folder and in its subfolders one level down (DCIM/<folder>/<image>), so a picker can offer the console's camera folder as well as the app's own. Subfolder entries are folder/name; the caller joins dir + "/" + entry.

Verification

test_attach: 27 checks, 0 failures (new cases: nested entries sorted, two levels down not listed, a missing folder returns 0). Clients (Indigo, Cobalt) build against this branch in their own PRs.

Docs

Header comment on the function; CHANGELOG entry.

Changelog: CHANGELOG.md

Checklist

• CI is green (CI gate and flow / conventions)
• No secrets, tokens or signing keys in the diff
• Tests added or changed with the behaviour; none skipped, disabled or deleted

🤖 Generated with Claude Code

[ewanc26]

Superseded by #194: same commit on a fresh branch from main, because this one conflicted with the v0.38.2 release and a rebase would need a force-push.