feat: add descriptions to risk bundle table headers

[sirakinb]

Fixes #233.

Summary

• Add hover descriptions to the risk bundle table headers users are most likely to need explained: APR, min/max amount, min/max duration, available capacity, balance, capacity, and stake usage.
• Apply the descriptions in both the protection purchase bundle selector and the risk-bundles overview table.
• Add English locale strings for the new table help text.

Testing

• python3 -m json.tool public/locales/en/application.json
• python3 -m json.tool public/locales/en/bundles.json
• Not run: JS build/test scripts, because this environment does not have npm/yarn/pnpm available and the fresh clone has no node_modules.

[sirakinb]

Small CI note: this PR is hitting the same CLA Assistant infrastructure failure as the other current Etherisc PRs.

The annotation is:

Could not retrieve repository contents. Status: 401

The workflow reads signatures from etherisc/cla-signatures via PERSONAL_ACCESS_TOKEN, so this appears to be a workflow credential/access issue rather than a code/test failure in this PR. Happy to complete the CLA step once the workflow can prompt/check it.

[sirakinb]

Maintainer note: the CLA Assistant check is failing before it can evaluate the PR. The workflow reports that it could not retrieve repository contents with status 401, which looks like a CLA Assistant token/app permission issue on the repository side rather than a code failure in this PR.