Deliver fixes for the three preexisting test failures reported in PR #24 #26

Context

The validation comment on #24 reported 80 passed / 3 failed, reproduced on master:

• test_alertfunctions.R: assert_that not found.
• test_timeseriespipeline.R: con not found.
• test-remove-tweet-historical-alerts.R: locked binding for read.parameters.

PR #20 already replaces the first two legacy scripts with isolated fixture-based tests and explicit database connections. Its integration of #19 now supplies explicit parameters/version dates to the historical-alert test, removing namespace binding mutation and direct sourcing of package files.

This issue tracks delivering those fixes to master alongside CI: #25.

Acceptance criteria

• The complete suite on the delivered branch has no failures or warnings.
• Historical alert tests exercise the loaded package without replacing locked bindings.
• Calendar and firstday regressions remain covered after integrating master.
• A successful CI run verifies the changes before delivery to master.

Local evidence on aaf7ab2: 297 passing expectations, 0 failures, 0 warnings, 1 PostgreSQL opt-in skip. Remote validation is pending. These are maintenance fixes for preexisting test failures, not regressions introduced by #24.