D198 — No recorded demo in the README

Status: implemented. Closes #268.

Context. The README opened with a vhs-recorded GIF of the CLI/TUI (docs/assets/demo.gif, produced by .github/vhs/record.sh). By the time #249 asked for a re-recording it predated the current TUI by six releases; #262 re-recorded it, and the next visible UX change would have made it stale again. Nothing checked it: unlike the tool names cited in the docs (D101's TestDocsToolNamesExist), a recording cannot fail CI when it drifts.

Decision. The README carries no recorded demo. The GIF, docs/assets/ and .github/vhs/ are removed; the product is shown by the text, the provider matrix and the mermaid diagram, which are edited in the same PR as the code they describe.

Rationale. A picture of the UX is documentation with no test and a toolchain (vhs, ffmpeg) outside the build, regenerated by hand. It drifted silently once and would again, and every clone carried ~210 KB of it. The first screen of the README is better spent on the Quick start.

Consequences. A future demo belongs outside the repository (a release note, the docs site) or comes with a way to go stale loudly. Re-adding one to the README reopens this entry.