Fix progress notification ordering in GetProjectStatsAsync

[Copilot]

Progress stage 2/3 notifications were emitted after their respective slow operations completed, meaning clients only saw updates once the work was already done.

Changes

• Stage 2 ("Computing dependency metrics") moved to before ComputeStatsAsync
• Stage 3 ("Summarizing results") moved to before JSON serialization and cache storage

// Before: notifications fired after the slow work
var stats = await statsService.ComputeStatsAsync(...);
progress?.Report(new ProgressNotificationValue { Progress = 2, ... }); // too late

// After: notifications fire before the slow work
progress?.Report(new ProgressNotificationValue { Progress = 2, ... });
var stats = await statsService.ComputeStatsAsync(...);

progress?.Report(new ProgressNotificationValue { Progress = 3, ... });
var json = JsonSerializer.Serialize(stats);
await cache.StoreAsync(...);

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[Copilot]

Pull request overview

This PR fixes progress notification timing in the MCP tool get_project_stats so clients receive stage updates before the corresponding slow operations run.

Changes:

• Emit progress stage 2 (“Computing dependency metrics”) before ComputeStatsAsync.
• Emit progress stage 3 (“Summarizing results”) before JSON serialization and cache storage.

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