docs: Add design touch-ups (#17505)

This PR adds several design tweaks to elements of the documentation,
most notably swapping the heading title font from `PPAgrandir` to
`Lora`, which makes the docs consistent with the new website. Aside from
this, there's also some tiny, low-hanging content adjustments to a few
pages.

--- 

Release Notes:

- N/A

docs/src/completions.md

@@ -15,7 +15,7 @@ When there is an appropriate language server available, Zed will by-default prov
 
 You can manually trigger completions with `ctrl-space` or by triggering the `editor::ShowCompletions` action from the command palette.
 
-For more information, see :
+For more information, see:
 
 - [Configuring Supported Languages](./configuring-languages.md)
 - [List of Zed Supported Languages](./languages.md).

docs/src/contribute-to-zed.md

@@ -12,4 +12,4 @@ If you're wanting to contribute by building out a feature, we recommend taking a
 
 ## Zed GitHub Repository
 
-Our codebase can be found [here](https://github.com/zed-industries/zed).
+Check [our codebase out on GitHub](https://github.com/zed-industries/zed).

docs/src/repl.md

@@ -4,7 +4,7 @@
 
 Bring the power of [Jupyter kernels](https://docs.jupyter.org/en/latest/projects/kernels.html) to your editor! The built-in REPL for Zed allows you to run code interactively in your editor similarly to a notebook with your own text files.
 
-<figure style="overflow: hidden; border-top-left-radius: 2px; border-top-right-radius: 2px;">
+<figure style="width: 100%; margin: 0; overflow: hidden; border-top-left-radius: 2px; border-top-right-radius: 2px;">
     <video loop controls playsinline>
         <source
             src="https://customer-snccc0j9v3kfzkif.cloudflarestream.com/aec66e79f23d6d1a0bee5e388a3f17cc/downloads/default.mp4"