Prepare v0.1.x release metadata and final release checklist

[andywkff]

Summary

Prepare the repository for the next v0.1.x release by aligning changelog/release notes, roadmap/checklist state, and final verification evidence after the recent portfolio orchestration and documentation/tutorial work.

Scope

• update CHANGELOG.md with unreleased additions/changes that are actually in the worktree history
• prepare current v0.1.x release notes without assuming the final tag prematurely
• sync ROADMAP.md release lane with validated status
• refresh local task tracking/review notes
• rerun build/test verification and record the result

Non-goals

• creating or moving git tags
• publishing GitHub release notes
• performing the final public announcement

[andywkff]

Release-prep pass is complete.

What changed:

• updated CHANGELOG.md with the unreleased portfolio orchestration + documentation/tutorial completion work
• prepared docs/RELEASE_NOTES_v0.1.x.md without forcing the final tag name prematurely
• updated README.md, docs/INDEX.md, ROADMAP.md, docs/RELEASE_CHECKLIST.md, and tasks/todo.md so the release lane and docs all tell the same story

Verification:

• swift build
• swift build -c release
• swift test (122 tests, 0 failures)
• swift run BacktestingKitTrialDemo
• bash tools/parity/run_parity.sh correctly reported that no local JS engine checkout is present, so parity remains an environment-dependent gate in this worktree rather than a package regression

Still intentionally manual:

• create the final release tag
• publish the GitHub release notes
• announce the parity baseline / required JS engine revision for contributors