[ZeroPoint95]

Changes

• Files dropped on the new-tab start page now draw a removable attachment chip row above the composer the moment the drop lands, so the attachment is visible, can be removed (backspace on the empty box or a click on the chip), and no longer stays invisible until the chat opens.
• The tray's draw and press share one geometry helper (welcomeUnitBox) and the same chip labels, resolved through the welcome unit's own row marks, so a click's column is the painted column; the conversation's chipTrayTarget refusal for the start page is untouched.
• Adds the missing docs/changes/unreleased change entry for PR 1912 that the check job's changelog gate requires, and restores the two low-credit tests to the fix: honor free-route opt-out throughout credit recovery #1905-gated path (test-only repair).
• Final change: 5 files, +230/−18.

Closes #1827.

Validation

• Proof · 8 of 8 claims shown locally. GitHub CI is checked after publishing.
• ✓ The required check failure was solely the missing change entry: every other step in that job's log passed (go build ./..., go vet ./..., make fmt-check, manual generate+packed test, changes check), and the run exited on the changelog gate ('This pull request adds no entry in docs/changes/unreleased/', exit 1).
• ✓ The light gate failure is derivative of the required check run: its step asserts 'light gate: failure; touched packages: success', i.e. the gate mirrors the check job's status, so the entry fixes it with it.
• ✓ Added docs/changes/unreleased/1912-newtab-drop-tray.md (kind fixed, surface [chat], with an invalidates line naming the invisible-drop belief that is no longer true), and make changelog-check passes on the current checkout.

by codeaf factory

Factory-Approval: evt_b9aea2af @ZeroPoint95 2264fc2