docs: reconcile README/PRD/ROADMAP/ARCHITECTURE/AGENTS with the shipped v0.2.2 state

[voyvodka]

Problem

The audit's most pervasive cross-cutting finding was documentation/version drift — docs that contradict the shipped product, which erodes trust even where the code is correct. Several are copy-paste hazards.

Fixes (each verified against the real code/config)

README.md

• Manual docker run example used ConnectionStrings__WebhookDb; the engine reads ConnectionStrings__Default (appsettings.json + the config table). A reader's docker run would have failed.
• The general curl / SDK / Prometheus examples used the local-dev port 5128, but the Docker Quick Start (the recommended path) is 5100 — a Docker user copy-pasting them hit the wrong target. They now use 5100 (matching Quick Start and the SDK's own default base URL). The "Local Development" section keeps 5128 (correct for dotnet run).
• "Run all tests (215 tests)" → the count is removed (it was a hard-coded number that drifts; actual is now 251).

docs/PRD.md — payload transformation removed from the MVP non-goals (it shipped post-MVP via ADR-003); "Last Updated" bumped.

docs/ROADMAP.md — "Latest release" synced from v0.2.0 → v0.2.2 (with the v0.2.1 hardening + portal-package release noted); @webhookengine/endpoint-manager (B1 Step 7) marked done (portal-v0.1.0, 2026-05-11) instead of "planned". Launch/blog roadmap items left untouched.

docs/ARCHITECTURE.md — §2 solution structure now lists the shipped AuditLogs / Portal / DashboardPortal controllers (were omitted); the duplicate ### 3.5 heading is fixed (HTTP Delivery Service is now ### 3.8, giving a clean 3.1–3.8 sequence).

AGENTS.md — frontend stack line corrected from "TypeScript 5.9 + Vite 7" to TypeScript 6 + Vite 8 (matches src/dashboard/package.json).

Notes

• .planning/ is gitignored (maintainer's local notes) so it isn't part of this PR; it's refreshed separately.
• The SDK <Version> lag (0.2.0 vs the platform line) is intentionally left to release-prep, not changed here.
• Final of the five post-audit critical-fix PRs (impact order): portal client → SDK contract → concurrency tests → security baseline → doc-truth.