Modernize the toolchain: Scala 2.13.16, JDK 21, Apache Pekko, and wider PostgreSQL support#1383

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GeekOfWires wants to merge 7 commits into

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GeekOfWires:stack-modernization

Commits on Jul 18, 2026

Phase 0: bump Scala, sbt, and low-risk dependencies

GeekOfWires
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claude
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Phase 1: migrate Akka 2.6.20 -> Apache Pekko 1.1.x

GeekOfWires
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Phase 2: move build/runtime/CI to JDK 21

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Phase 3: widen PostgreSQL version support (keep current, enable newer)

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Add missing Default import in LocalActionTest

GeekOfWires
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Enable server runtime on JDK 21: Kamon 2.7.7, Kanela 2.1.1, logback 1.5.18

GeekOfWires
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claude
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Fix Docker image tag; run compose stack on JDK 21 / Postgres 18

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claude
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