Deduplicate layout script tags and enforce JS dependency order

## Why
Multiple PRs repeatedly surfaced duplicate script includes and dependency-order regressions across layouts.

## Evidence
- PR #58 reviews: duplicate includes (`main.js`, `command-palette.js`) and missing `utils.js`/`search-manager.js` in some layouts.
- PR #62 review: duplicate `command-palette.js` include noted in teaching layout.

## Scope
- Audit `_layouts/*.html` for duplicated script tags.
- Ensure dependency order: `utils.js` and `search-manager.js` load before scripts that consume them.
- Remove redundant includes in affected layouts (`teaching`, `teaching-course`, `team`, `research`, `history` as needed).
- Add a small CI guard script/check to catch duplicate includes and order violations.

## Acceptance Criteria
- No layout has duplicate includes for `main.js` or `command-palette.js`.
- Pages depending on `window.Utils` and `window.SearchManager` always load those first.
- CI fails when duplicate includes or invalid ordering is introduced.