Add project setup, map overlays, and automated releases

[sammeltassen]

Adds a complete slides init / slides create flow with title and optional Protomaps-key prompts, an English example, and package scripts. Projects without a basemap configuration now use a plain background, and development runners generate their TypeScript configuration before starting Vite.

Adds global GeoJSON layer defaults and custom MapLibre layers, including labels drawn from feature properties. Slides resolve their overrides independently and use native opacity transitions. Map fitting now supports contain, cover, and equal, with a configurable inner margin. Space and layers-panel visibility controls repaint reliably after zooming while preserving authored opacity and normal control activation.

Removes the obsolete warped-map image mode, unused configuration fields, app helpers, and dependencies. Updates authoring and migration documentation, software credits, and changesets. The template submodule points to its existing published commit; uncommitted content-repository changes are not included.

Combines npm trusted publishing, tagging, and GitHub release creation in release.yml. Publication runs from the npm environment on main only after a version change. Changesets still prepares a separate version PR; this PR does not bump the package version. Required PR checks continue reporting success for documentation-only changes, while code changes run the full integration checks.

Validation:

• 223 unit tests passed across the workspace, plus the native renderer alignment test.
• Package TypeScript checks and Svelte checks passed with zero errors or warnings, including the committed template checkout used by CI.
• Development smoke test passed: isolated sites, hot reload, content and asset updates, IIIF generation, configuration changes, and shutdown.
• Fresh-package smoke test passed: packed installation, project initialization, type checking, dev server, native thumbnails, IIIF, subpath URLs, and repeat production builds.
• Frozen lockfile validation and git diff --check passed.