Add Sandstem

**Font Project Git Repo URL:**

https://github.com/timcogan/sandstem

**Super short description of the Font Family:**

Sandstem is a rounded sans serif family derived from Quicksand under the SIL Open Font License. It keeps the feel of the original design, renames the family to avoid the Quicksand reserved name, and adds a clearer serifed uppercase `I` for better differentiation from lowercase `l` and other vertical strokes. This is helpful for educational material or other content where a clear representation of `I` is critical.

**Requirements:**

By opening this issue, I confirm the project meets the following requirements:

- [x] The entire font project is available in a Github repository (repo) and licensed under the [OFL](https://openfontlicense.org/open-font-license-official-text/)
- [x] The source files are available in the repo
- [x] I am the sole copyright author of the Sandstem modifications, and the upstream Quicksand work is licensed under the OFL. I commit to clearly disclosing if AI tools were used in the creation of this project.
- [x] There is a Reserved Font Name in the upstream project: "Quicksand". It is used only for attribution and is not used in whole or in part in this family name. The modified family name is Sandstem.
- [x] The family name is unique according to [namecheck.fontdata.com](https://namecheck.fontdata.com/)
- [x] The name of the font family expected to appear on app menus is clearly communicated and definitive: Sandstem. It does not include any copyright holder's full name or acronym.
- [x] The font supports at least the Google Fonts 'Latin Core' glyphset from [github.com/googlefonts/glyphsets](https://github.com/googlefonts/glyphsets) ([direct link](https://github.com/googlefonts/glyphsets/blob/main/data/results/txt/nice-names/GF_Latin_Core.txt))
- [x] The repo has the [Google Fonts preferred upstream repo structure](https://googlefonts.github.io/gf-guide/upstream.html)
- [x] I have read, agree with, and comply with, the full [Google Fonts contributing requirements](https://googlefonts.github.io/gf-guide/index#pre-production-getting-your-fonts-ready-for-gf)
- [x] I will maintain the repository and participate in the onboarding process (addressing, solving, and responding to issues, merging pull requests, etc)

Additional notes:

`Sandstem` is a Modified Version of `Quicksand`. The upstream Quicksand Reserved Font Name is respected: the family is not named Quicksand, and the name Quicksand appears only for attribution to the original project.

AI tools were used to assist with repository cleanup and planning. The `Sandstem` source, release files, and design decisions are maintained by Tim Cogan.

**Image:**