Add CI verification tests and guidelines

[menny]

• Update AGENTS.md with new testing and dependency pinning guidelines
• Implement Kotlin verification test using JUnit 5
• Implement TypeScript verification test using Node.js native test runner
• Configure Bazel targets for all verification tests
• Use copy_to_bin for configuration file hermeticity in Bazel

[github-actions]

• [Risk] [.github/workflows/review.yml:28] We are removing the reviewer_github_token from the Cassandra AI Review job. If the action requires this token to authenticate and post comments back to the Pull Request, this change will break the automated review feedback loop. We should ensure the action can operate with the default GITHUB_TOKEN permissions before removing this secret.
• [Maintenance] [backend/BUILD.bazel:15-18] The backend_test target uses ConsoleLauncher with a hardcoded --select-package septima argument. This is fragile; any tests added to sub-packages (e.g., septima.auth) or different package structures in the future will be silently ignored by the test runner. We should configure the test runner to discover all tests within the srcs of the target automatically.
• [Maintenance] [tools/prettier_filter_links.sh:18] The fallback path for PRETTIER_BIN hardcodes the _main workspace name. Since our MODULE.bazel defines the module name as septima, this path may be invalid in certain Bazel environments or future versions. We should rely exclusively on the PRETTIER_BIN environment variable passed via the sh_binary and fail explicitly if it is not set, rather than attempting to guess the runfiles layout.
• [Observation] [.editorconfig:12] We are changing the Kotlin indentation from 4 spaces (the language standard) to 2 spaces. While this is consistent with the rest of the project's move toward 2-space indentation, it may conflict with default IDE configurations for Kotlin. We should ensure all contributors update their IDE settings to prevent "format wars" in future PRs.
• [Observation] [backend/Main.kt:2] Manual indentation change to 2 spaces. As noted in the AGENTS.md guidelines, we should generally rely on bazel run //:format (which now uses ktfmt as per tools/format/BUILD.bazel) rather than manual adjustments, but this change is correct according to the new policy.

The consolidation of agent instructions via symlinks for CLAUDE.md and GEMINI.md is a great improvement for maintainability.

❌ Rejected