fix: check daily if update is due based on UPDATE_INTERVAL

[aaronspruit]

Originally updates would only be checked if they need to happen based on the duration of UPDATE_INTERVAL. This means that if the container is restarted, it resets the timer.

This change compares the timestamp on DATA_DIR/.photon-index-updated to the UPDATE_INTERVAL on a daily basis.

I believe this was the originally intended functionality, as by default it means the container needs to be running for 30 days before an update is even attempted...instead of doing updates every UPDATE_INTERVAL.

I was very confused as to why my service hadn't updated when the last time it did so was Feb 17th and UPDATE_INTERVAL=30d (even with bouncing the container). This fix correctly identified that today it's 45 days out of date and did the update.

$ task check
task: [deadcode] uv run vulture --min-confidence 100 --exclude ".venv" .
task: [format] uv run ruff format
task: [lint] uv run ruff check --fix
task: [typecheck] uv run ty check
All checks passed!
17 files left unchanged
All checks passed!

$ task test
task: [test] uv run pytest
================================================= test session starts =================================================
platform linux -- Python 3.13.12, pytest-9.0.2, pluggy-1.6.0
rootdir: /mnt/c/Users/rebel/repos/photon-docker
configfile: pyproject.toml
plugins: cov-7.0.0
collected 36 items                                                                                                    

tests/utils/test_regions.py ...................                                                                 [ 52%]
tests/utils/test_sanitize.py ......                                                                             [ 69%]
tests/utils/test_validate_config.py ...........                                                                 [100%]

================================================= 36 passed in 2.99s ==================================================