feat: convert to npm workspaces monorepo with per-package publishing

[alexluckett]

The problem

@defra/interactive-map currently ships as a single npm package where map provider dependencies (maplibre-gl, @arcgis/core, ol, etc.) are declared as optional peer dependencies at the package root.

A single package.json cannot declare different peer dependencies for different sub-path exports. A consumer installs interactive-map but npm has no knowledge of whether they're using the MapLibre or ESRI provider — npm's checks run at a different level. The result: any consuming service can silently drop a required map provider and npm won't flag the breakage. In the case of forms-engine-plugin, maplibre-gl was almost accidentally dropped with no build-time error — the build would have succeeded and failed only at runtime, potentially in production.

The only way to make maplibre-gl a required peer dependency of the MapLibre provider — without also forcing ESRI consumers to install it — is to give each provider and plugin its own published package.

Solution

Converts the repository to an npm workspaces monorepo. Each provider and plugin becomes its own scoped npm package with required peer dependencies based only on what that package actually needs. The existing file hierarchy, CI pipeline, and build system remain architecturally consistent — publishing gains a loop to publish each package individually.

New package naming convention:

@defra/interactive-map                       # core
@defra/interactive-map-provider-maplibre     # provider: maplibre
@defra/interactive-map-plugin-draw-ml        # plugin: draw-ml
@defra/interactive-map-plugin-search         # plugin: search

Benefits:

• Install-time enforcement of required dependencies via native npm tooling
• Consumers install only what they use — core can get smaller over time
• Clearer naming: the package name tells you whether something is a provider or plugin
• Future flexibility: mature plugins/providers can be spun off into their own repo with independent version numbers

What changed

• Each provider and plugin gains its own package.json with scoped name and required peer deps
• The beta/ directory is dropped — beta status is now signalled via publishConfig.tag: "beta" per package rather than file hierarchy
• scripts/publish-package.sh extended to stamp lockstep versions into all workspace packages and publish each one
• Rollup and webpack build paths updated for the flattened directory structure
• Datasets maplibre adapter added as a separate rollup entry, enabling the ./adapters/maplibre sub-path export
• Four direct node_modules/ import paths in draw-ml replaced with public MapboxDraw API equivalents
• Fixed a bug in the publish script where npm publish --prefix was silently publishing the root package instead of each workspace package

Consumer migration

The only breaking change is the import path. Update sub-path imports to the new package names:

Before	After
@defra/interactive-map/providers/maplibre	@defra/interactive-map-provider-maplibre
@defra/interactive-map/plugins/interact	@defra/interactive-map-plugin-interact
@defra/interactive-map/plugins/search	@defra/interactive-map-plugin-search
@defra/interactive-map/plugins/datasets/adapters/maplibre	@defra/interactive-map-plugin-datasets/adapters/maplibre
(and so on for each plugin/provider)