view: remove dead code

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Found in the review of #2057, which adds the experimental view. Paths refer to #2059's head.

Summary

Code the view no longer uses:

Rust: ViewReduce and ViewNode.reduce are always None. The page's reduceOpSchema is a strict enum while Rust would send op: String. Remove both, with the model contract changes.
Rust: a debugging eprintln! in crates/graphcal-project/src/view_model/tests.rs.
web/view/src/engine.ts (about 80 lines): evaluateProject, evaluationSchema, engineValueSchema, EngineValue, Evaluation, Prepared.evaluateReport, and the "evaluated" branch of outcomeSchema. Keep the parts that decode a failed prepare.
replaceExpr in web/view/src/source.ts, the fallback in editExpr for a model with no expr_range. It is unreachable in practice, and wrong: replaceExpr("param n2: Int = 2;", 1, "2", "5") returns param n5: Int = 2;.
The re-export in web/view/src/project.ts, Project.fileOf, Project.packageName, Explorer.setTitle and drag.moved.
Remnants of the removed tiers in web/view/src/wires.ts, with their stale comments.
In web/view/src/layout.ts: ownAxis, PackedZone.height, and a header comment that contradicts the code.
An unreachable !inBand branch in web/view/src/render.ts.
Unused CSS classes: .row-key, .zone-output, .ruler-unrolled.
Playground entries in web/view/.gitignore, and the unused build script in web/view/package.json.