Drop Microsoft.ApplicationInsights — telemetry is a no-op

[ChrisonSimtian]

Telemetry.cs short-circuits because InstrumentationKey = "" (per the rebrand note: original NUKE key was matkoch-owned, we don't reuse). The Microsoft.ApplicationInsights PackageVersion is dead weight until we stand up a Fallout-owned endpoint.

Drop the package + the unused fields/methods in Telemetry.cs that reference TelemetryClient. When a Fallout telemetry backend lands, re-introduce.

Refs the dependency audit. Done when:

• PackageVersion removed from Directory.Packages.props
• PackageReference (if direct) removed
• TelemetryClient s_client and call sites either removed or stubbed
• Build clean, tests pass

[ChrisonSimtian]

Closed in 97ea857 — Microsoft.ApplicationInsights gone from Directory.Packages.props + Fallout.Build.csproj. TelemetryClient field removed, TrackEvent stubbed to no-op. Public callers unchanged so a future Fallout-controlled backend can wire back through without touching call sites.