fix(renderer): respect text z-index ordering

[Komzpa]

Summary

• decouple text/icon collision priority from canvas paint order
• evaluate text/icon/shield candidates from high to low z-index, then replay accepted canvas commands from low to high z-index
• add a regression test for both reported cases: high-z text wins collisions over low-z icons, and allow-overlap features paint high-z labels last

Fixes #63.

Validation

• npm test

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Measure text with pending style updates

The command recorder defers style assignments (including font) until replay(), but recorder.measureText() calls ctx.measureText() immediately against the live canvas state. In _renderTextAndIcons, text/shield collision checks and placement run before replay, so widths are computed with stale fonts whenever a feature sets a different font size/family, which can incorrectly reject labels or allow overlaps. This regression is introduced by the new recording path and affects any map with mixed text styles.

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