Update contributing guidelines and enhance build scripts: Add detailed instructions for build modes in CONTRIBUTING.md, clarifying the use of incremental and full rebuilds. Revise package.json to streamline build commands and introduce new dev scripts for better development workflow. Remove deprecated integer arithmetic chapter files and update curriculum JSON to reflect the latest structure. Enhance Pythagorean theorem content with a new vocabulary section for improved clarity.

CONTRIBUTING.md

@@ -23,6 +23,8 @@ Thank you for helping grow free, open textbooks.
 
 **Search locally:** After `bun run build:js`, run `bun run index:search` once (or again after changing chapter HTML), then `zola serve`. Try [http://127.0.0.1:1111/search/](http://127.0.0.1:1111/search/) or press ⌘K / Ctrl+K.
 
+**Build modes:** `bun run build` is smart/incremental for local iteration; use `bun run build:full` for a deterministic full rebuild (CI/release checks).
+
 ---
 
 ## How the catalog fits together
@@ -228,9 +230,12 @@ Omit `banner` for subjects that should stay unchanged (e.g. roadmap-only placeho
 bun install
 bun run sync:chapters  # after content/ chapter changes
 bun run build:js       # sync + Vite
+bun run dev            # incremental sync + watch + zola serve
+bun run dev:full       # force full sync before dev
 zola serve
 bun test
 bun run build
+bun run build:full
 ```
 
 - Do **not** commit `themes/openfreebooks/static/` (Vite output).