ci: remove HTML coverage report to eliminate mismatched data warning (#66)

## Summary
- Remove HTML coverage report generation from CI workflow
- The "36 functions have mismatched data" warning was caused by `cargo
llvm-cov report --html`, a known upstream LLVM/Rust issue
- Codecov uses `lcov.info` directly and provides a better UI, making the
HTML report redundant in CI
- The `coverage-report` recipe remains in justfile for local development
- Switch mise.toml from `ubi` to `github` backend for cargo-binstall

## Test plan
- [x] Coverage workflow runs without warnings
- [x] lcov.info still generated and uploaded to Codecov

Author: tylerbutler

.github/workflows/coverage.yml

@@ -31,9 +31,6 @@ jobs:
       - name: Run tests with coverage
         run: just test-coverage
 
-      - name: Generate HTML coverage report
-        run: just coverage-report
-
       - name: Upload to Codecov
         uses: codecov/codecov-action@b9fd7d16f6d7d1b5d2bec1a2887e65ceed900238 # ratchet:codecov/codecov-action@v4
         with:
@@ -45,6 +42,4 @@ jobs:
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # ratchet:actions/upload-artifact@v4
         with:
           name: coverage-report
-          path: |
-            lcov.info
-            target/llvm-cov/html/
+          path: lcov.info

mise.toml

@@ -2,4 +2,4 @@
 just = "latest"
 ruff = "latest"
 
-"ubi:cargo-bins/cargo-binstall" = "1"  # Latest 1.x
+"github:cargo-bins/cargo-binstall" = "1"  # Latest 1.x