Prepare v4.0 release #175

Goal

Prepare the user-requested major release v4.0, covering the complete investment redesign and all other changes shipped since v3.3.

Scope

• Audit merged PRs and direct commits since v3.3, including the investment epic's child changes.
• Write grouped release highlights, complete changelog coverage, and migration/upgrade instructions.
• Set the root application and lockfile versions to 4.0 and update README release links.
• Run the release checks and create a release PR plus a draft GitHub release with identical notes.
• Merge and publish only after explicit user approval; deployment remains separate.

Completion criteria

• Every shipped change since v3.3 is covered by the changelog with source links.
• Root package and both root lockfile version fields agree on 4.0.
• README, changelog and draft release notes agree, including all six new SQL migration files and upgrade requirements.
• Required tests, types, production build and lint pass on the pinned Node 22 runtime; the client suite also passes on available Node 26.
• Release PR and draft release are ready for review.
• After separate approval, the published release targets the reviewed merged release commit and its UTC publication date agrees with the changelog.

References

• Previous release: https://github.com/apptrackit/finance/releases/tag/v3.3
• Investment integration: Rebuild Investments with cash-linked trades, performance and portfolio history #147
• Release process: https://github.com/apptrackit/finance/blob/main/.github/RELEASE_GUIDE.md