Add V3 streaming event ingestion pipeline

[ejsmith]

Summary

• add controller-free V3 Minimal API routes that stream top-level JSON values directly from HttpRequest.BodyReader using source-generated System.Text.Json metadata
• move raw stack parsing and fingerprint generation to the server, with .NET, Java, JavaScript, Python, caused-by, manual-stacking, and normalized fallback support
• resolve discarded stacks before quota reservation/materialization so discarded events take the cheapest path and are not charged
• add distributed atomic quota reservation, deterministic event IDs, inline bulk persistence, ambiguous-write reconciliation, and a durable asynchronous side-effect work item
• make stack statistics, notifications/webhooks, and post-save plugin work replay-safe with stable identities and per-event completion markers
• add bounded microbatches, concurrency/backpressure, cancellation, gzip/Brotli support, compressed/decompressed/event/request limits, ProblemDetails, observability, and disabled-by-default allowlist rollout controls
• publish an isolated V3 OpenAPI document, HTTP samples, architecture/rollout documentation, BenchmarkDotNet suites, and a repeatable streaming load harness
• pin Microsoft.OpenApi 2.7.5 to remediate CVE-2026-49451 discovered during dependency validation

API and compatibility

V3 is a new breaking-contract surface:

• POST /api/v3/events
• POST /api/v3/projects/{projectId}/events
• Content-Type: application/x-ndjson
• one complete top-level JSON event per stream item; top-level arrays are rejected

The V2 controller, payload formats, queued handoff, and response contract remain available and unchanged. V3 is disabled by default and can be rolled out by project or organization allowlist.

Verification

• dotnet build Exceptionless.slnx --no-restore --disable-build-servers -m:1 -v:minimal — 0 warnings, 0 errors
• full backend suite — 2,350 passed, 0 failed, 2 intentional performance fixtures skipped
• focused V3 persistence/replay/outbox suite — 26 passed
• focused ingestion/compatibility suite — 85 passed
• BenchmarkDotNet dry run — all 10 ingestion benchmarks executed
• NuGet transitive vulnerability audit — no vulnerable packages in all eight projects
• git diff --check — clean

Rollout

Keep this PR in draft while reviewing the architecture and running the documented one-, two-, four-, and eight-instance load matrix against the intended Redis/Elasticsearch topology. Production activation remains a configuration-only, reversible step.

Closes #2368

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Exceptionless.AppHost	38%	39%	144	❌
Exceptionless.Core	74%	66%	10512	➖
Exceptionless.Insulation	45%	38%	308	❌
Exceptionless.Web	84%	68%	7227	✔
Summary	77% (24625 / 31978)	66% (11352 / 17227)	18191	✔