feat: add saved run history and deletion

[SerDrozd]

Summary

Add local run history so previous reconciliation results can be reopened and removed when they are no longer needed.

Changes

• add a paginated /runs history page ordered newest first
• show source files, row counts, and current reconciliation status counts
• add a Runs link to the application header
• allow previous reconciliation results to be reopened
• add an explicit confirmation page before deleting a saved run
• delete the selected run and its related source rows, matches, and review events through existing database cascades
• keep deletion isolated so other saved runs are unaffected

Validation

• uv run ruff check .
• uv run mypy src tests
• uv run pytest - 58 passed
• uv build
• git diff main...HEAD --check
• manual browser smoke test for run history and delete confirmation