skills: point consumer skills at given: instead of #(filter)

[jswir]

malloy-model and malloy-notebooks already mark #(filter) legacy and document given: as the replacement. Four consumer-facing skills were never updated and still present #(filter) as the current mechanism:

• malloy-analyze — tells the agent to add a #(filter) to the source when the analysis needs a knob the model doesn't expose.
• malloy-define — instructs the agent to write #(filter) annotations into a model it is authoring. This is the one that actually produces new #(filter) in new models.
• malloy-document — its annotation table and its #(filter) section both describe it as current, and point at a malloy-model section heading that no longer exists under that name.
• malloy-analysis-report — same as malloy-analyze, for reports.

Each now points at given: and names the two exceptions malloy-model already documents — required and implicit — so the guidance doesn't overshoot into cases given: cannot cover yet.

Found while following malloy-reproducible-analysis on a real analysis: the model-authoring path recommended #(filter) with nothing marking it deprecated, and the stale cross-reference in malloy-document sent the reader to a heading that had already been renamed to Legacy: Parameterizable Filters.

Docs only, no code. Independent of #1079 — no overlapping files.

[jswir]

Superseded by #1079, which carries this commit cherry-picked unchanged (87597a24).

Folding it there rather than merging separately: it was unreviewed, it is the same class of change as that PR, and it was the last thing blocking the skills PR that retires malloy-analyze — one of the four files this touches.