docs: add 0.1.2 release notes

planning/releases/0.1.2.md

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+# compose2pod 0.1.2 — accept the service `hostname` key
+
+A patch release that stops rejecting valid compose documents which set a
+service `hostname`. The validator was over-strict: a service carrying
+`hostname:` — used to give a service a stable name that other services connect
+to — raised `unsupported key 'hostname'`. Such documents now convert.
+
+## Fix
+
+- **The service `hostname` key is accepted.** `validate()` no longer rejects a
+  service that sets `hostname:`, and the hostname is made resolvable to
+  `127.0.0.1` inside the pod, exactly like a network alias: it joins the
+  `--add-host` set so other services reach the service by that name. Because all
+  services share one network namespace (and the pod's UTS namespace), only name
+  resolution is meaningful — no per-container `--hostname` is emitted.
+
+## Downstream
+
+No action needed — additive and backward compatible. Documents that previously
+failed with `unsupported key 'hostname'` now emit a pod script; nothing that
+converted before changes.
+
+## Internals
+
+- `architecture/supported-subset.md` adds `hostname` to the supported
+  service-key matrix with the shared-namespace resolution rationale.
+- 86 tests at 100% line coverage (enforced); `ruff select=ALL`, `ty`, and
+  `eof-fixer` clean.