fix: use local date for dashboard budget

[hadamrd]

Summary

• Make the dashboard budget "today" calculation use the operator-local date instead of UTC date.
• Fixes the local-midnight failure where tests seed time.strftime("%Y-%m-%d") but _today_iso() was still on the prior UTC day.

Testing

• PYTHONPATH=src /Users/k.majdoub/repos/forge-loop/.venv/bin/python -m pytest -q tests/test_dashboard.py::test_budget_today_sums_costs_per_issue tests/test_dashboard.py::test_budget_view_renders_today_spend -> 2 passed
• PATH="$HOME/.local/bin:$PATH" uv run ruff check src tests -> passed
• PATH="$HOME/.local/bin:$PATH" uv run mypy src/forge_loop/ -> passed, no issues in 157 source files
• PATH="$HOME/.local/bin:$PATH" uv run pyright src/forge_loop -> 0 errors
• GH_TOKEN="$(gh auth token)" PYTHONPATH=src /Users/k.majdoub/repos/forge-loop/.venv/bin/python -m pytest -q -> 2140 passed, 2 skipped