docs: refresh Star History badge and chart (#9945)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - The README is the first project surface most prospective users and
contributors see
> - The existing Star History presentation only showed one static chart
at the bottom of the page
> - The project also lacked the compact Star History Rank badge
alongside its other top-level badges
> - The chart should respect the reader's light or dark color scheme
while preserving the existing history link
> - This pull request adds the rank badge and replaces the chart with
responsive light/dark sources
> - The benefit is a more useful, theme-aware project-growth snapshot in
both prominent README locations

## Linked Issues or Issue Description

No public GitHub issue exists for this documentation request.

- **Problem / motivation:** The README's Star History presentation is
less visible than the other project badges and its chart does not adapt
to light and dark themes.
- **Proposed solution:** Add Star History's rank badge to the centered
badge row and use the provider's responsive `<picture>` markup for the
chart section.
- **Alternatives considered:** Keeping the current single static chart
would avoid markup changes but would not provide theme-aware rendering
or the requested rank badge.
- **Roadmap alignment:** Documentation-only presentation change; it does
not add or duplicate a product roadmap item.
- **Related PR:** #9922 refreshed the surrounding README roadmap content
before this focused follow-up.

## What Changed

- Added the Star History Rank badge to the README's centered badge row.
- Replaced the single Star History image with light- and dark-theme
chart sources using the supplied sealed chart URL.
- Preserved the existing Star History destination and accessible chart
label.

## Verification

- `git diff --check`
- Confirmed the badge, light chart, and dark chart endpoints each return
HTTP 200.
- Rendered the updated section through GitHub's GFM API and confirmed
GitHub preserves the linked `<picture>` and both theme sources.
- Confirmed the diff contains only `README.md`.

## Risks

- Low risk: documentation-only change with no runtime, API, dependency,
or migration impact.
- The chart depends on Star History's hosted badge/chart endpoints and
supplied sealed token remaining available.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI `gpt-5.4` via Codex CLI; context-window size not exposed by the
runtime; medium reasoning with repository, shell, GitHub API, and live
HTTP verification tools.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

README.md

@@ -14,6 +14,7 @@
 <p align="center">
   <a href="https://github.com/paperclipai/paperclip/blob/master/LICENSE"><img src="https://img.shields.io/badge/license-MIT-blue" alt="MIT License" /></a>
   <a href="https://github.com/paperclipai/paperclip/stargazers"><img src="https://img.shields.io/github/stars/paperclipai/paperclip?style=flat" alt="Stars" /></a>
+  <a href="https://www.star-history.com/paperclipai/paperclip"><img src="https://api.star-history.com/badge?repo=paperclipai/paperclip" alt="Star History Rank" /></a>
   <a href="https://discord.gg/m4HZY7xNG3"><img src="https://img.shields.io/discord/000000000?label=discord" alt="Discord" /></a>
 </p>
 
@@ -468,7 +469,13 @@ MIT &copy; 2026 [Paperclip Labs, Inc](https://paperclip.ing)
 
 ## Star History
 
-[![Star History Chart](https://api.star-history.com/image?repos=paperclipai/paperclip&type=date&legend=top-left)](https://www.star-history.com/?repos=paperclipai%2Fpaperclip&type=date&legend=top-left)
+<a href="https://www.star-history.com/?repos=paperclipai%2Fpaperclip&type=date&legend=top-left">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/chart?repos=paperclipai/paperclip&type=date&theme=dark&legend=top-left&sealed_token=hFjuwFq41bQD5cevvXVv5cTru2swWRZujwJYKlHhtBh6n0H5-VvJZW2SAlcQKB8u4KxhyEB9JqFg1yccJ8WLv9wPBcoWpWcak4gx0MYTWu_pOs2jKOaDluH7KsLeTKt6DHGkHiN3LsqV9s--MTDQcC6Xl7zV51W0-YezQXo-pVPgoFDFAGf2CY5fiP5Q" />
+    <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/chart?repos=paperclipai/paperclip&type=date&legend=top-left&sealed_token=hFjuwFq41bQD5cevvXVv5cTru2swWRZujwJYKlHhtBh6n0H5-VvJZW2SAlcQKB8u4KxhyEB9JqFg1yccJ8WLv9wPBcoWpWcak4gx0MYTWu_pOs2jKOaDluH7KsLeTKt6DHGkHiN3LsqV9s--MTDQcC6Xl7zV51W0-YezQXo-pVPgoFDFAGf2CY5fiP5Q" />
+    <img src="https://api.star-history.com/chart?repos=paperclipai/paperclip&type=date&legend=top-left&sealed_token=hFjuwFq41bQD5cevvXVv5cTru2swWRZujwJYKlHhtBh6n0H5-VvJZW2SAlcQKB8u4KxhyEB9JqFg1yccJ8WLv9wPBcoWpWcak4gx0MYTWu_pOs2jKOaDluH7KsLeTKt6DHGkHiN3LsqV9s--MTDQcC6Xl7zV51W0-YezQXo-pVPgoFDFAGf2CY5fiP5Q" alt="Star History Chart" />
+  </picture>
+</a>
 
 <br/>