fix(ci): Enable CPU profiling and add dotnet tools to PATH

- Add dotnet tools directory to PATH for subsequent steps
- Switch from --providers to --profile cpu-sampling for actual CPU profiling
- This generates flamegraphs with real stack traces instead of empty traces

Previous approach only captured runtime events (GC, JIT) without CPU samples.
The cpu-sampling profile includes Microsoft-DotNETCore-SampleProfiler which
captures stack traces at 1ms intervals, enabling proper performance analysis.

Tested locally with act - generates 22KB trace with actual profiling data.

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

Author: neil-pozetroninc

.github/workflows/dotnet.yml

@@ -102,6 +102,8 @@ jobs:
           dotnet-version: 8.0.x
       - name: Install dotnet-trace
         run: dotnet tool install --global dotnet-trace
+      - name: Add dotnet tools to PATH
+        run: echo "$HOME/.dotnet/tools" >> $GITHUB_PATH
       - name: Restore Dependencies
         run: dotnet restore ProbotSharp.sln
       - name: Restore HelloWorldBot
@@ -146,7 +148,7 @@ jobs:
         run: |
           echo "Collecting trace from HelloWorldBot process..."
           echo "TMPDIR is set to: $TMPDIR"
-          dotnet-trace collect --name HelloWorldBot --providers Microsoft-Windows-DotNETRuntime --duration 00:00:30 -o trace.nettrace || (echo "Trace collection failed!" && exit 1)
+          dotnet-trace collect --name HelloWorldBot --profile cpu-sampling --duration 00:00:30 -o trace.nettrace || (echo "Trace collection failed!" && exit 1)
       - name: Convert trace to Speedscope format
         run: dotnet-trace convert trace.nettrace --format Speedscope
       - name: Upload flamegraph artifact