v0.3.4 — co-resolution release for pipeline-core 3.3.0

0.3.4 — co-resolution release for pipeline-core 3.3.0.

• Requires views-pipeline-core>=3.3.0: the first pipeline-core whose reporting stage looks up each comparison model's metrics under that model's own data/generated (PerModelMetricFrameSource, vpc #485). With older pipeline-core, baseline and constituent rows were silently absent from every evaluation report that declared them — ensemble and single-model subjects alike (register C-215). Locked-layout paths are unchanged; only the root per model moved.
• Requires views-evaluation>=2.0.0 (pandas-free); the MetricFrame surface this repo consumes is unchanged.
• Seam contract test corrected to pin the per-model source (the old test locked the defective subject-rooted construction); a real two-root on-disk round-trip test added.
• CM choropleth now refuses (loudly, ValueError) a frame carrying two country_ids under one ISO code instead of silently drawing one of them (C-227).
• PosteriorDistributionAnalyzer.print_summary(file=None): the default stream is now resolved to the current sys.stdout at call time, so contextlib.redirect_stdout and pytest capture are respected. Passing file explicitly is unchanged (#260).
• Inherited from views-evaluation 1.1.0 (their ADR-015 R9), not a change in this repo: AP on a group with no positive truth is now nan rather than 0.0. views-evaluation's MetricFrame mean row is a nanmean and excludes such groups, so AP means read from reports can shift for sparse targets.
• Still on views-frames 1.x (<2.0.0). views-frames 2.0.0 is gated by two ceilings — ours and the views-frames<2 cap on views-evaluation 2.0.0's [frames] extra; a separate qualification follows.
• views-transformation-library, stepshift and xarray leave the resolved dependency closure (pipeline-core 3.3.0 dropped the first; the other two arrived through it). views-reporting never imported any of them.

No new views-reporting features. Full changes: #280–#285, #291–#299.