Fix HybridQueryRanker commonMain compile for v0.5.0 publish (#479)

`MutableMap.putIfAbsent` is JVM-only and breaks
`:ampere-core:compileCommonMainKotlinMetadata`, which is what the
publish.yml workflow runs on tag push. The regular PR CI doesn't run
that task, so the issue slipped through when AMPR-156 (#476) merged and
only surfaced when the v0.5.0 tag triggered the publish workflow.

Swap to `getOrPut`, which is in commonMain and has the same effect
(insert if absent, leave existing alone) when the return value is
discarded inside `forEach`.

Verified with `./gradlew :ampere-core:compileCommonMainKotlinMetadata`
and the existing HybridQueryRankerTest.

Commit authored by Claude Opus 4.7 on Miley's behalf.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: wow-miley

ampere-core/src/commonMain/kotlin/link/socket/ampere/knowledge/HybridQueryRanker.kt

@@ -61,7 +61,7 @@ class HybridQueryRanker(
         // semantic hit so its enrichment wins ties (semantic queries usually
         // walk the document table; keyword search may not).
         val canonicalById = mutableMapOf<String, KnowledgeQueryResult>()
-        keywordResults.forEach { canonicalById.putIfAbsent(it.chunk.id, it) }
+        keywordResults.forEach { canonicalById.getOrPut(it.chunk.id) { it } }
         semanticResults.forEach { canonicalById[it.chunk.id] = it }
 
         return canonicalById.values