core: one Dispatcher for the facades' request plumbing - #79

Summary

• The 0.3.0 retrospective listed "8× duplicated facade plumbing": every domain facade assembled the interceptor chain, recorded fanar.model / http.method / http.url and ran InterceptorChainImpl in its own private dispatch. That lives in one qa.fanar.core.internal.dispatch.Dispatcher now (0.4.0 plan, Phase 6); each facade's dispatch is a one-line delegation and the class owns only its endpoint, wire format and decoding. Net −104 lines.
• Internal refactor under ADR-018 — no ADR, no behaviour change: facade constructors, FanarClient and all eight *ClientImplTests are untouched (each facade builds its own Dispatcher from the same arguments). http.url is now read from the request the facade built rather than its endpoint field — always the same URI, including the per-name voice delete.
• The dispatcher gets its own package instead of the plan's internal.transport: RetryInterceptor already imports from internal.transport, so placing it there would have made retry ↔ transport cyclic. DispatcherTest proves attribute order, the omitted model attribute, chain order (a user interceptor sees the bearer header the built-in set) and null arguments; ARCHITECTURE, PROJECT_STATE and CHANGELOG updated.

Type of change

• Bug fix
• New feature / capability
• New module
• Refactoring (no behavior change)
• Breaking change
• Documentation / tooling / CI only

Test plan

• mvn verify passes locally
• Live tests pass against the real Fanar API (if applicable, with FANAR_API_KEY set)
• GraalVM --self-test passes (if the SDK's reflective surface changed)

Reviewer checklist

• Public API changes are intentional, documented in javadoc, and an ADR was added/updated if the design changed
• Which *IntegrationTest proves the behaviour this PR claims? (100 % JaCoCo on a unit is not proof of wiring — see CONTRIBUTING "Testing")
• Breaking changes carry @Deprecated(since, forRemoval = true) and a migration path in the PR description
• BOM updated if modules were added or removed
• No third-party types leak into qa.fanar.core public API
• If a non-obvious project decision was made, capture it in memory/ so future contributors find it