docs: replace manual contributor list with auto-updating grid

CONTRIBUTORS.md required contributors to append their own handle, which added
friction to every PR and would drift the moment someone forgot. The README now
renders the contributors graph directly, so recognition is automatic.

Drops the file and the three references to it in README, CONTRIBUTING, and
ARCHITECTURE.

Author: AnayDhawan

ARCHITECTURE.md

@@ -46,7 +46,6 @@ studymap/
 ├── CHANGELOG.md
 ├── CODE_OF_CONDUCT.md
 ├── CONTRIBUTING.md
-├── CONTRIBUTORS.md
 ├── LICENSE
 ├── README.md
 ├── SECURITY.md

CONTRIBUTING.md

@@ -132,8 +132,8 @@ Optional scope in parens: `feat(calendar): add today label`. One logical change
 
 ## Get recognized
 
-First merged PR? Add your GitHub handle to [CONTRIBUTORS.md](CONTRIBUTORS.md), in the
-same PR or a quick follow-up.
+Nothing to do. Once your PR is merged, your avatar appears in the Contributors
+section of the [README](README.md) automatically.
 
 ## House rules
 

CONTRIBUTORS.md

@@ -72,7 +72,9 @@ New here? Start with an issue tagged [`good first issue`](https://github.com/Stu
 
 ## Contributors
 
-See [CONTRIBUTORS.md](CONTRIBUTORS.md).
+Thanks to everyone who has added a place, fixed the map, or improved the docs.
+
+[![Contributors](https://contrib.rocks/image?repo=StudentSuite/StudyMap)](https://github.com/StudentSuite/StudyMap/graphs/contributors)
 
 ## License