Make bundled COSMIC toplevel protocol subset DTD-valid

[c-wri]

Observed

wayland-scanner emits a validation warning for protocol/clipreg-cosmic-toplevel-v1.xml:

Element interface content does not follow the DTD, expecting
(description? , (request | event | enum)+), got
WARNING: XML failed validation against built-in DTD

The warning points at the intentionally opaque zcosmic_workspace_handle_v1 declaration:

<interface name="zcosmic_workspace_handle_v1" version="1"/>

Desired invariant

Bundled protocol descriptions used by the canonical native build should be wire-compatible with the supported COSMIC v1 boundary and valid input to the supported wayland-scanner, without validation warnings.

Investigation / acceptance

• Recover the authoritative v1 workspace-interface shape from upstream COSMIC protocol history rather than inventing wire messages.
• Preserve the existing design goal: ClipReg binds only the v1 toplevel-info surface it needs and does not pull newer v2/v3 workspace/foreign-toplevel dependencies into the runtime without an observed need.
• wayland-scanner client-header and private-code complete without DTD warnings.
• make check remains green and generated protocol output remains untracked.
• Keep this separate from issue Daemon can become permanently non-responsive after repeated operations #1 / PR Prevent self-owned selection deadlock after paste #2 unless investigation proves it participates in the liveness defect.

This warning is not currently classified as a v0.2.0-rc.1 blocker.