chore: release 0.2.0; document the store contract and on_send_error

Bump tines-core and tines-sim to 0.2.0 (Peer::in_flight changed type).
Add CHANGELOG.md. README gains a "Writing a store" section and a note on
calling Exchange::on_send_error when driving Exchange without Node.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,57 @@
+# Changelog
+
+All notable changes to the tines crates. Versions follow
+[Semantic Versioning](https://semver.org/); before 1.0, a minor bump may break
+the API.
+
+## 0.2.0 — 2026-10-18
+
+Hardening from a full-codebase review. Wire-compatible with 0.1.0 except
+where noted.
+
+### Added
+
+- `Exchange::on_send_error`: rolls back the last `next_frame` after a failed
+  send. `Node::poll` calls it, so a `Busy` or `Unreachable` frame is retried
+  instead of being lost.
+- `Store::for_each_addressed_id`, with a default that visits every id.
+  `MemStore` overrides it, so custody no longer reads every broadcast
+  observation on each poll.
+- `Bloom::fold`, and `Bloom::from_parts` now accepts any power-of-two length up
+  to `SUMMARY_BYTES`. Summaries are folded to fit the transport's MTU; a
+  0.1.0 node rejects a folded summary, so mixed-version links only sync when
+  the MTU allows a full 512-byte filter.
+- `InFlight`, describing a fragment stream in progress.
+
+### Changed
+
+- **Breaking:** `Peer::in_flight` is now `Option<InFlight>` (was
+  `Option<(ObservationId, u8)>`).
+- Custody (addressed) and broadcast sending alternate per peer, and addressed
+  candidates are taken in rotation.
+- Bounce suppression lasts one contact, as the addressed-delivery spec says.
+
+### Fixed
+
+- A fragment stream could panic, or send corrupt fragments, when the
+  observation's age changed encoded length mid-stream or the tick went
+  backwards.
+- Summaries larger than the MTU stopped all broadcast sync on narrow links.
+- A full bounce table silently stopped recording, so one addressed message
+  was re-sent on every poll and starved broadcast.
+- An addressed send interrupted another peer's fragment stream, which was
+  then never finished.
+- An addressed message that couldn't fit the MTU blocked every other
+  addressed message for that peer.
+- A duplicate addressed message was forwarded back to the carrier that sent
+  it.
+
+### CI
+
+- Tests, clippy and docs also run without the `alloc` feature; doc warnings
+  fail the build; `--locked` everywhere; toolchain pinned to 1.99.0; actions
+  pinned to commit SHAs.
+
+## 0.1.0
+
+Initial release: `tines-core` and `tines-sim`.