Add Fresh Harvest integration scaffold

Implements the freshharvest.com two-step login handshake, config flow,
6-hour polling coordinator, and four delivery sensors. Portal page parsing
is not implemented; async_get_next_delivery raises until the account HTML
is mapped against a signed-in session.

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project are documented here.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- Config flow taking freshharvest.com portal credentials.
+- Session client implementing the two-step login handshake against
+  `/s/popup/login` and `/s/submit/login`, including the per-session
+  `LoginSecurity` and `SubmitToken` anti-replay fields.
+- Update coordinator polling every 6 hours, surfacing auth failures as
+  `ConfigEntryAuthFailed` so Home Assistant prompts for re-authentication.
+- Sensor platform for next delivery date, order total, order status, and box
+  item count.
+
+### Known limitations
+
+- Delivery parsing is unimplemented; the integration cannot yet produce values.
+  The portal HTML has not been mapped against a signed-in session.
+- The signed-in check is a provisional heuristic and needs confirming against a
+  real authenticated response.