refactor(compaction): moved compaction APIs to @oh-my-pi/pi-agent-core

- Relocated compaction, branch-summarization, pruning, and utils from coding-agent to packages/agent/src/compaction.
- Moved OpenAI remote compaction helpers from packages/ai to the new compaction module.
- Added handoff.ts with extractHandoffDocument, createHandoffContext, and renderHandoffPrompt helpers.
- Exposed new entries.ts with standalone SessionEntry types so coding-agent no longer owns them.

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -1,6 +1,7 @@
 import * as fs from "node:fs/promises";
 import * as os from "node:os";
 import * as path from "node:path";
+import { CompactionCancelledError, type CompactionOutcome } from "@oh-my-pi/pi-agent-core/compaction";
 import {
 	getEnvApiKey,
 	getProviderDetails,
@@ -37,7 +38,6 @@ import { buildHotkeysMarkdown } from "../../modes/utils/hotkeys-markdown";
 import { buildToolsMarkdown } from "../../modes/utils/tools-markdown";
 import type { AsyncJobSnapshotItem } from "../../session/agent-session";
 import type { AuthStorage } from "../../session/auth-storage";
-import { CompactionCancelledError, type CompactionOutcome } from "../../session/compaction";
 import type { NewSessionOptions } from "../../session/session-manager";
 import { outputMeta } from "../../tools/output-meta";
 import { resolveToCwd, stripOuterDoubleQuotes } from "../../tools/path-utils";