Move plugin-contract.md into README's Building plugins section; remove docs/, repoint all references

plugins/scheduling/README.md

@@ -1,6 +1,6 @@
 # Scheduling — the reference plugin
 
-A worked example of the [plugin contract](../../docs/plugin-contract.md). Copy this folder, rename
+A worked example of the [plugin contract](../../README.md#building-plugins). Copy this folder, rename
 it (the folder name becomes the plugin id and mount path), and point it at your own backend.
 
 What it demonstrates:

plugins/scheduling/plugin.ts

@@ -1,6 +1,6 @@
 // Reference plugin: a worked example of the contract — a list page that fetches upstream
 // data, a CSRF-guarded form that forwards a write upstream, and permission-gated nav. Copy this
-// folder, rename it, point it at your own backend. Full contract: docs/plugin-contract.md.
+// folder, rename it, point it at your own backend. Full contract: README.md → Building plugins.
 
 import { definePlugin } from "../../src/plugin-host/plugin-api.ts";
 import { assertHttpUrl, createShift, createUpstream, listShifts, newShiftForm, overview, READ, SCHEDULING_PATH, SHIFTS_PATH, WRITE } from "./shifts.ts";

plugins/scheduling/shifts.ts

@@ -3,9 +3,9 @@
 // host renders. The plugin holds no state of its own (README "Stateless") — data lives upstream.
 //
 // Handlers are factories bound to a ShiftsUpstream, and `fetch` is injectable, so they unit-test as
-// pure functions against a mock upstream with no network (docs/plugin-contract.md → dev/test story).
+// pure functions against a mock upstream with no network (README.md → Local dev & test story).
 
-// One import from the host's plugin-api barrel — the stable author surface (see docs/plugin-contract.md).
+// One import from the host's plugin-api barrel — the stable author surface (see README.md → Building plugins).
 import { can, CSRF_FIELD, GuardError, type PageChrome, parseListQuery, readFormBody, type RouteHandler, tracedFetch } from "../../src/plugin-host/plugin-api.ts";
 
 export const SCHEDULING_PATH = "/scheduling"; // the plugin's public overview page