Ship the batch: undo, parallel subagents, lazy MCP, hot-reloaded skills; docs and CI/CD

Loop and ergonomics batch across Now/Next and Maintenance:
- /undo and /redo via pre-prompt file snapshots (snapshot.ts)
- task takes a tasks[] array and runs investigations concurrently (subagent.ts)
- lazy MCP tools: mcp_list/mcp_inspect/mcp_call meta-tools, eager opt-in (mcp.ts, config.ts)
- skill tool reads its list live so a mid-session install is callable next turn (skills.ts)
- tool-name lists (tool-kinds.ts) derived from a mutating() marker; gates previously ungated writes
- prune/session recovery path summarized, and step-back doom-loop primitive (step-back.ts)
- @file completion re-walks on a slow cooldown; estimateTokens and pricing labeled as estimates

Docs: README, CHANGELOG, docs/{mcp,architecture,development} updated to match.
CI/CD: bun install-store cache and concurrency gates on both workflows; release.yml now
composes file-based release notes via scripts/make-release-notes.ts and verifies every binary.

test/complete-ui.test.tsx

@@ -1,27 +1,15 @@
 import { expect, test } from 'bun:test';
 import { render } from 'ink-testing-library';
 import React from 'react';
-import { MockLanguageModelV4, simulateReadableStream } from 'ai/test';
+import { MockLanguageModelV4 } from 'ai/test';
 import { Session } from '../src/session';
 import { App, createApprovalBridge } from '../src/ui/App';
-import { testHooks, usageOf } from './helpers';
+import { streamOf, testHooks, textChunks, usageOf } from './helpers';
 
 const usage = usageOf(3);
 
 const model = new MockLanguageModelV4({
-  doStream: async () =>
-    ({
-      stream: simulateReadableStream({
-        chunks: [
-          { type: 'text-start', id: '0' },
-          { type: 'text-delta', id: '0', delta: 'reply' },
-          { type: 'text-end', id: '0' },
-          { type: 'finish', finishReason: { unified: 'stop', raw: 'stop' }, usage },
-        ],
-        chunkDelayInMs: null,
-        initialDelayInMs: null,
-      }),
-    }) as any,
+  doStream: async () => streamOf(textChunks('reply', usage)),
 });
 
 const paths = ['README.md', 'src/app.ts', 'src/session.ts', 'src/ui/App.tsx', 'test/session.test.ts'];