Standardize on "OpMode" / "linear OpMode" / "iterative OpMode" / "Blocks OpMode"

The upcoming 9.0 release of the SDK will switch all usages of the term OpMode to the form "OpMode". FTC Docs does not consistently use the form "OpMode", and should be updated to do so.

Additionally, the preferred way to refer to OpModes that specifically extend `LinearOpMode` (including Blocks OpModes) is **"linear OpMode"**, and the preferred way to refer to OpModes that specifically extend `OpMode` directly is **"iterative OpMode"**.

No files or tests are named. Search the FTC Docs repository for inconsistent OpMode terminology, using the preferred forms in the issue as the checklist and reviewing each match in context. Done means the documentation consistently distinguishes OpMode, linear OpMode, iterative OpMode, and Blocks OpMode.

Written by the indexing model from the issue text.