chore: address review cleanup

[stefan-jansen]

Address review cleanup backlog.

[Copilot]

Pull request overview

This PR performs “review cleanup” maintenance across CI/release automation and labeling logic, including a behavioral fix to trend_scanning_labels to avoid defaulting flat/no-trend cases to a negative label.

Changes:

• Adjust trend_scanning_labels to emit null labels (and associated outputs) when no directional trend is detected; add a regression test for flat price series.
• Pin GitHub Actions dependencies (by commit SHA where applicable) and pin uv to a fixed version; update CI/docs workflows to pass explicit --python to uv sync.
• Housekeeping: relax the numpy upper bound in uv.lock, fix a test comment, and remove an unreferenced docs SVG asset.

Reviewed changes

Copilot reviewed 7 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
uv.lock	Updates numpy upper-bound constraint.
tests/test_new_labeling_methods.py	Adds regression test for null-label behavior in flat/no-trend trend scanning.
tests/features/volatility/test_volatility_comprehensive.py	Corrects Bollinger Bands test comment to match behavior.
src/ml4t/engineer/labeling/horizon_labels.py	Changes trend scanning labeling to avoid default -1 when best_t == 0; nulls out t_value when appropriate.
docs/images/ml4t_ecosystem_workflow_color.svg	Removes the SVG asset (no in-repo references found).
.github/workflows/release.yml	Pins uv version; pins PyPI publish action to a commit SHA.
.github/workflows/docs.yml	Pins uv version; pins deploy action to a commit SHA; passes explicit --python to uv sync.
.github/workflows/ci.yml	Pins uv version; passes explicit --python to uv sync across jobs.
.github/dependabot.yml	Switches Dependabot ecosystem from pip to uv for uv.lock updates.

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