Add examples for DynamicProxy, Pooling, DotGraph, and multitenant ASP.NET Core

[tillig]

Part of #32

First half of item 8. The middleware example for autofac/Documentation#160 follows separately, alongside the documentation changes it needs.

Proposed Changes

Four shipping packages had no example at all. Now they do.

Example	Shows
DynamicProxyExample	Interception wired two ways: named on the registration, and declared with [Intercept] on the contract
PoolingExample	Instance reuse across lifetime scopes, plus a pool policy that resets an instance on return
DotGraphExample	Capturing a resolve operation as a Graphviz graph
AspNetCoreMultitenantExample	Per-tenant registration overrides in ASP.NET Core, tenant taken from the query string

Each one is registered in Examples.slnx, has a launch configuration, a README, and a row in the root README table.

Choices worth reviewing

PoolingExample is built around its own output. A pooled registration looks like a singleton until you can see otherwise, so the example prints a line per construction and reports which instance each scope received. Sequential scopes share one instance; overlapping scopes each construct their own. The use count printed after reuse is 1 rather than 2, which is the proof that the policy reset the instance on its way back into the pool — that reset is the actual difference between pooling and SingleInstance.

DotGraphExample registers a decorator on purpose. A graph of three unrelated services is not worth rendering; an adapter chain is.

AspNetCoreMultitenantExample writes its own ITenantIdentificationStrategy. The package deliberately ships none — I checked the public surface rather than assuming, since the package README shows a QueryStringTenantIdentificationStrategy that the reader is expected to supply. The example also covers the case people get wrong: a tenant with no registered override falls back to the container default rather than failing.

DynamicProxyExample shows both wiring styles side by side, because "which one do I use" is the question, and either one alone reads like the only option.

Verification

All 19 projects build with 0 errors and 0 warnings in Release under the analyzer rules from #37, and both gates pass. Every example was executed:

• DynamicProxyExample — both interceptor styles log the call and the return value.
• PoolingExample — 2 connections constructed across 4 resolves, use count reset on return.
• DotGraphExample — emits a .dot file, and I rendered it with Graphviz to confirm it actually parses rather than just looking plausible.
• AspNetCoreMultitenantExample — no tenant and ?tenant=gamma both resolve the default; alpha and beta resolve their own overrides.

The launch configurations are checked with the same validator from #38: 11 configurations, 11 launchable projects, nothing missing and nothing orphaned. All 95 markdown links resolve, with repo links verified against each clone's origin remote and doc links mapped back to .rst files in the Documentation repo.