feat(context,infra): compression pipeline stages 4-5 — token pruning + relevance + ToMe

- build() is now suspend: pipeline runs all stages in fixed order, each gated by level
- TOKEN_PRUNE (level 3): TokenPruner interface + LLMLingua-2 sidecar (sidecars/llmlingua)
  + HttpTokenPruner adapter (fails open if sidecar down); prunes freeform, preserves
  protected spans, skips tier-0 turns when TIER_SPLIT on
- TOME_MERGE (level 8): ToMeMerger collapses near-duplicate freeform turns (Jaccard)
- Stage 5 selection: RelevanceScorer + EmbeddingRelevanceScorer (cosine over Embedder);
  query-conditioned reorder so least-relevant freeform drops first under budget
- [orchestration] compression_level + token_pruner_url config, wired in Main
- suspend ripple fixed across builder callers/stubs

infrastructure/compression/build.gradle

@@ -0,0 +1,24 @@
+plugins {
+    id 'java-library'
+    id 'org.jetbrains.kotlin.jvm'
+    id 'org.jetbrains.kotlin.plugin.serialization'
+}
+
+ext {
+    ktor_version = '3.0.3'
+}
+
+dependencies {
+    implementation project(':core:context')
+    implementation "org.slf4j:slf4j-api"
+
+    implementation "io.ktor:ktor-client-core:$ktor_version"
+    implementation "io.ktor:ktor-client-cio:$ktor_version"
+    implementation "io.ktor:ktor-client-content-negotiation:$ktor_version"
+    implementation "io.ktor:ktor-serialization-kotlinx-json:$ktor_version"
+    testImplementation "org.junit.jupiter:junit-jupiter"
+    testImplementation "io.ktor:ktor-client-mock:$ktor_version"
+    testImplementation "org.jetbrains.kotlin:kotlin-test"
+}
+
+tasks.named("koverVerify").configure { enabled = false }