Emit explicit original skill images in saved draft offer rows

Draft offer rows now emit #s<skillId># alongside the existing selection ID so the native client can resolve original skill artwork and show its existing skill tooltip. The reminder, frozen saved offers, preview, Learn/Back and Later flow stay server-owned. Selection IDs remain 32-bit, and successful claims still grant current rank 1 with maximum mastery.

Pair with the client-10 merge request. Related to #10 (closed); implementation/contract notes are in docs/draft-skill-images.md.

Validation: full Java compilation, the existing disposable server/draft/save-reload/commit-fault suite, and the updated 22-assertion Nashorn presentation fixture pass. The paired client passes original-asset rendered hover, wrapping/scrolling, clipping, missing-description and tooltip cleanup checks. Combined server/client branches also pass integration checks. These are isolated/synthetic and rendered fixtures, not live campaign gameplay or deployment. Default base: 76e344abd7e7f5720dd0e634ae2a728e4e8da6cc.

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