Capture waterway linestrings in the OSM rivers query

[drussellmrichie]

The built-in rivers query only matched polygon water areas (water=river/stream). Rivers and streams mapped as waterway linestrings — how rivers are commonly represented in OSM — were missed, so proximity-to-rivers enrichment under-counted them. This adds the waterway river/stream tags. Additive; no existing behavior removed.

Adds a test asserting the rivers tag set includes waterway.

[github-actions]

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