fix(post-location): fix map rendering and marker on new posts

[techtimo]

Summary

• Leaflet CSS not loaded on new posts — enqueue_block_editor_assets() called enqueue_styles() which bails early via should_enqueue() when the post has no Spotmap block yet. Replaced the call with a direct wp_enqueue_style() so the CSS is always loaded in the editor.
• Tiles overflowing the map container — added overflow: hidden and position: relative to the map container div (belt-and-suspenders, since Leaflet CSS also sets this on .leaflet-container). Without CSS loaded, tiles bled outside the div and sat on top of the Clear location button, causing apparent click misses and tiny coordinate shifts from accidental map clicks.
• BeautifyIcon marker — replaced the default Leaflet PNG marker (broken URL in editor context) with L.BeautifyIcon using the POST type config from spotmapjsobj.marker (thumbtack icon by default, respects admin customisation).

Test plan

• Open a brand-new post in the block editor — map renders correctly, tiles stay inside the container, attribution is visible
• Click on the map to set a location — BeautifyIcon thumbtack marker appears
• Drag the marker — coordinates update
• Click Clear location — marker disappears, coordinates cleared
• Open an existing post with a Spotmap block — no regression in map or block behaviour

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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