feat(reminders): support operator-triggered runs

[Aaronontheweb]

Summary

• add daemon-backed netclaw reminder run <id> for immediate reminder execution
• track scheduled vs manual execution source in runtime completion and history
• preserve scheduled semantics for one-shot reminders and scheduled failure accounting

Validation

• dotnet test src/Netclaw.Actors.Tests/Netclaw.Actors.Tests.csproj --filter "FullyQualifiedName~Reminder"
• dotnet test src/Netclaw.Daemon.Tests/Netclaw.Daemon.Tests.csproj --filter "FullyQualifiedName~ReminderEndpointAuthorizationTests"
• dotnet test src/Netclaw.Cli.Tests/Netclaw.Cli.Tests.csproj --filter "FullyQualifiedName~ReminderCommandTests"
• dotnet slopwatch analyze
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify
• git diff --check
• openspec validate manual-reminder-execution --type change

Notes

• full dotnet test --no-restore could not complete locally because the filesystem hit 100% and MSBuild failed with No space left on device
• ./evals/run-evals.sh requires eval target credentials that are not configured in this environment