Improve readme and clarify examples

[JesseHerrick]

MyApp.Repo was a poor example for hover docs. Repo functions do resolve correctly, but ironically there are no docs on the injected functions, thus nothing to show, but this isn't a bug in Dexter. This PR changes this to use MyApp.Accounts as a better example.

Also adds the missing Emacs section to the Table of Contents.

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Note

Low Risk
Low risk documentation-only change; no code paths or runtime behavior are modified.

Overview
Updates README.md to improve clarity of documentation examples by switching the sample module/function names from MyApp.Repo to MyApp.Accounts (including delegate/hover/CLI examples) and refreshing the cursor-resolution and rename walkthroughs accordingly.

Also fixes small README hygiene issues (adds missing Emacs link in the table of contents and a trailing comma in the VS Code settings JSON snippet).

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