fix: resolve all post-merge compile errors

- Fix unresolved imports (auto_compaction, AutoCompactionEvent)
- Add Thinking/RedactedThinking match arms
- Fix workspace.dependencies serde_json
- Fix enum exhaustiveness in OutputContentBlock matches
- cargo check --workspace passes

rust/crates/plugins/Cargo.toml

@@ -7,7 +7,7 @@ publish.workspace = true
 
 [dependencies]
 serde = { version = "1", features = ["derive"] }
-serde_json = "1"
+serde_json.workspace = true
 
 [lints]
 workspace = true