docs(#94): CHANGELOG + README download/install for 1.1.2-beta.1

- CHANGELOG.md seeded with the 1.1.2-beta.1 entry (Added / Fixed / Known issues).
- README gains a "Download & Install" section for end users (Releases link,
  extract + run on Windows with the SmartScreen note, sideload the APK) — the repo
  previously had only developer build-from-source steps.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,30 @@
+# Changelog
+
+All notable changes to Offband Meshcore. Pre-releases are tagged `-beta.N` / `-rc.N`.
+
+## [1.1.2-beta.1] - 2026-06-24
+
+First public beta.
+
+### Added
+- Observer config + MQTT broker editor: field-at-a-time SET with enabled-last
+  activation, honest enable/disable that verifies the device actually applied the
+  change, and broker runtime-state + resolved-default hints (#80, #89, #93).
+- Cross-platform file logging to a rotating file under the app support directory,
+  with "Open logs folder" (desktop) / "Share logs" (mobile) on the log screen (#97).
+- Friendlier repeater path-hash labels (#90).
+- Self-contained Windows packaging that bundles the VC++ runtime so the zip runs on
+  a clean machine (#96).
+
+### Fixed
+- Channel sync advances immediately on a device error instead of stalling on empty
+  channel slots (#82).
+- The BLE connect handshake retry is capped with backoff so it can't churn the
+  connect or starve the contact-list load (#88).
+
+### Known issues
+- Companion message-sync may miss public history after a long offline gap (#91); a
+  firmware-side fix is in progress.
+- MQTT broker / Observer features require the firmware currently in review.
+
+[1.1.2-beta.1]: https://github.com/OffbandMesh/meshcore-client/releases/tag/v1.1.2-beta.1

README.md

@@ -20,6 +20,14 @@ Offband Meshcore is a cross-platform mobile application for communicating with M
   </tr>
 </table>
 
+## Download & Install
+
+> **Public beta** — expect rough edges; please [report bugs](https://github.com/OffbandMesh/meshcore-client/issues). Grab the newest build from [**Releases**](https://github.com/OffbandMesh/meshcore-client/releases).
+
+- **Windows (x64):** download `OffbandMeshcore-*-win-x64.zip`, extract it anywhere, and run `offband_meshcore.exe`. The beta is unsigned, so Windows SmartScreen will warn — click **More info → Run anyway**.
+- **Android:** download the `.apk` and install it (you may need to allow "install from unknown sources").
+- **iOS / macOS / Linux:** build from source for now — see [Getting Started](#getting-started).
+
 ## Features
 
 ### Core Functionality