docs: 0.7.0 release notes — middleware guide + Epic 3 closed

Docs-only release. Calls out the new docs/middleware.md page, notes the
non-goals (no source changes, no new built-in middleware, no docs-site
infra), and records Epic 3 as closed end-to-end after v0.4 + v0.7.

Author: lesnik512

planning/releases/0.7.0.md

@@ -0,0 +1,36 @@
+# httpware 0.7.0 — Middleware extension guide (docs-only)
+
+**0.7.0 is a docs-only release. No API changes.** Code written against 0.6.0 continues to work unchanged.
+
+This release ships the final piece of Epic 3 — a user-facing guide to writing custom middleware against `httpware`'s Middleware protocol. With it, Epic 3 (Resilience) closes.
+
+## What's new
+
+- **[`docs/middleware.md`](../../docs/middleware.md)** — a new top-level docs page covering:
+  - The `Middleware` Protocol and `Next` type alias, both exported from `httpware.middleware`.
+  - The three phase decorators (`@before_request`, `@after_response`, `@on_error`) as ergonomic shortcuts for the common cases.
+  - A worked `RequestIdMiddleware` example — assign a per-call UUID, propagate via `X-Request-Id`, log it alongside the response status. Placed outside `Retry` so all attempts of one call share one ID, and correlates naturally with the 0.6.0 observability events' `url` attribute.
+  - A "when NOT to write a middleware" section pointing redaction at `logging.Filter`, URL/header validation at `httpx2`, per-call behavior at `request.extensions=`, and HTTP-level tracing at `opentelemetry-instrumentation-httpx`.
+
+Plus small touchups so the guide is discoverable: a nav entry in `mkdocs.yml`, a one-sentence pointer in the README, and a "Where to go next" bullet in `docs/index.md`.
+
+## What's not in this release
+
+- No source code changes. The `Middleware` protocol, `Next` type, and phase decorators all already existed (shipped pre-0.4 via Epic 2); this release documents them.
+- No new built-in middleware (no CircuitBreaker, no RateLimiter, no metrics counter). The deliberate non-resilience worked-example choice keeps the guide focused on teaching the protocol rather than shipping a half-baked toy that gets cargo-culted.
+- No mkdocs publish workflow / docs-site infra. That's Epic 6 story `6-2`; this release just makes the strict build green.
+
+## Epic 3 closed
+
+Epic 3 (Resilience) has shipped end-to-end:
+- v0.4 slice 1 — `Retry` + `RetryBudget` + `attempt_timeout=`
+- v0.4 slice 2 — `Bulkhead`
+- v0.7 — extension-slot docs
+
+Remaining roadmap is Epic 6 (ship v1.0): `6-2` docs site infrastructure, `6-3` benchmarks, `6-5` release flow (Trusted Publishers + Sigstore).
+
+## References
+
+- Spec: [`planning/specs/2026-06-05-extension-slot-docs-design.md`](../specs/2026-06-05-extension-slot-docs-design.md)
+- Plan: [`planning/plans/2026-06-05-extension-slot-docs-plan.md`](../plans/2026-06-05-extension-slot-docs-plan.md)
+- Roadmap: [`planning/engineering.md`](../engineering.md) §8