feat(context): purify leading SYSTEM, route context layers as USER turns (#290)

Move intent, repo map, docs catalog, decision journal and relevant-files
context entries to EntryRole.USER so they no longer fold into the single
leading SYSTEM block — that block stays pure policy/schema. Omit L3 repo-map
retrieval on repair retries (the transcript already carries the evidence).
Add "initialIntent" to REQUIRED_SOURCE_TYPES.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

testing/kernel/src/test/kotlin/ContextFeedbackTest.kt

@@ -233,14 +233,14 @@ class ContextFeedbackTest {
     }
 
     @Test
-    fun `buildRelevantFilesEntry produces L3 system entry with Relevant files header`() {
+    fun `buildRelevantFilesEntry produces L3 user entry with Relevant files header`() {
         val hits = listOf(
             RepoKnowledgeHit(path = "src/Parser.kt", text = "src/Parser.kt: Parser, Lexer", score = 0.9f),
             RepoKnowledgeHit(path = "src/Main.kt", text = "src/Main.kt: main", score = 0.7f),
         )
         val entry = buildRelevantFilesEntry(hits)
         assertEquals(ContextLayer.L3, entry.layer)
-        assertEquals(EntryRole.SYSTEM, entry.role)
+        assertEquals(EntryRole.USER, entry.role)
         assertEquals("relevantFiles", entry.sourceType)
         assertTrue(entry.content.startsWith("## Relevant files"), "content: ${entry.content}")
         assertTrue(entry.content.contains("src/Parser.kt"), "content: ${entry.content}")