feat: timeline schema changes

[Jonathansumner]

Sub-branch (twig?) of #260

• Introduces schema changes to include timeline field
• Implements handler changes to reflect the new field
• Test coverage tweaked to incorporate new schema change

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Code Review Checklist (to be filled out by reviewer)

• Description accurately reflects what changes are being made.
• Either the PR references an issue (via the "Development" combobox) or the description explains the need for the changes.
• The PR appropriately sized.
• The PR contains an idempotent DB migration.
• I have verified the correctness of the DB migration using relevant data (e.g. test-generated data).
• New code has enough tests.
• New code has enough documentation to answer "how do I use it?" and "what does it do?".
• Existing documentation is up-to-date, if impacted.