refactor(acr): ACR Store 1 as a disposable memo, not a durable side-store (#305)

The shipped Store 1 persisted repo-file descriptors in a new SqliteObservationStore
— a second, unsynchronized SQLite writer on the event-log DB (no WAL/busy_timeout,
one shared Connection across coroutines) holding a fact the log already carries. That
violates "the event log is the only source of truth" (inv #1/#8): an Observation is
just FileWrittenEvent.path + postImageHash + describe(bytes).render(), and render is a
pure function of content-addressed CAS bytes.

Replace the whole durable apparatus with an in-process memo (descriptorMemo, keyed on
repoRoot+path+contentHash) on the orchestrator, next to the existing artifactContentCache.
Rebuilt from the log on restart, disposable, no external store. Preserves the perf win
(skip CAS read + regex on repeat describes) with none of the concurrency/lock risk.

Deletes: ObservationStore/InMemoryObservationStore/SqliteObservationStore (+ tests),
InfrastructureModule.createObservationStore, the FileReadTool priming path (which never
hit anyway — it keyed on a workspace-relative path while every consumer looks up the
absolute FileWrittenEvent.path), the FileReadConfig/SessionOrchestrator plumbing, and
five orphaned build.gradle deps.

Store 2 (soft-confidence hints) unchanged — it was correct.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HMbPmZZjcXhR2crU82zZ8S

infrastructure/src/main/kotlin/com/correx/infrastructure/InfrastructureModule.kt

@@ -53,10 +53,8 @@ import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
 import com.correx.infrastructure.router.turbovec.TurboVecL3MemoryStore
 import com.correx.infrastructure.router.turbovec.TurboVecSidecarConfig
-import com.correx.core.context.observation.ObservationStore
 import com.correx.infrastructure.persistence.SqliteEventStore
 import com.correx.infrastructure.persistence.artifact.LiveArtifactRepository
-import com.correx.infrastructure.persistence.observation.SqliteObservationStore
 import com.correx.infrastructure.tools.DefaultToolRegistry
 import com.correx.infrastructure.tools.DispatchingToolExecutor
 import com.correx.infrastructure.tools.SandboxedToolExecutor
@@ -108,12 +106,6 @@ object InfrastructureModule {
         )
     }
 
-    fun createObservationStore(dbPath: String = defaultDbPath): ObservationStore {
-        val dir = java.io.File(dbPath).parentFile
-        if (!dir.exists()) dir.mkdirs()
-        return SqliteObservationStore(DriverManager.getConnection("jdbc:sqlite:$dbPath"))
-    }
-
     fun createArtifactStore(rootDir: Path = Paths.get(defaultArtifactsRoot)): ArtifactStore {
         Files.createDirectories(rootDir)
         val index = SqliteArtifactIndex(rootDir.resolve("index.sqlite"))