feat: global exception handler, concurrent VLM, and docker security

- Add global FastAPI exception handler for unhandled errors
- Add get_current_user_obj() dependency for cleaner auth patterns
- Switch VLM image description from serial to asyncio.gather concurrency
- Extract score conversion to shared score_utils module
- Docker: use env vars for passwords, remove hardcoded API key default
- Add .gitattributes and update .gitignore for tar.gz and tsbuildinfo

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitattributes

@@ -0,0 +1,37 @@
+# Auto detect text files and perform LF normalization
+* text=auto
+
+# Source code - enforce LF line endings
+*.py text eol=lf
+*.ts text eol=lf
+*.tsx text eol=lf
+*.js text eol=lf
+*.jsx text eol=lf
+*.json text eol=lf
+*.css text eol=lf
+*.scss text eol=lf
+*.html text eol=lf
+*.md text eol=lf
+*.yml text eol=lf
+*.yaml text eol=lf
+*.toml text eol=lf
+*.sql text eol=lf
+*.sh text eol=lf
+*.bat text eol=lf
+*.conf text eol=lf
+*.cfg text eol=lf
+*.txt text eol=lf
+*.env text eol=lf
+
+# Binary files - don't touch
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.pdf binary
+*.zip binary
+*.woff binary
+*.woff2 binary
+*.ttf binary
+*.eot binary