feat: add xterm-zerolag-input standalone library

Extract Claudeman's local echo overlay into a reusable xterm.js addon
at packages/xterm-zerolag-input/. Provides instant keystroke feedback
via a DOM overlay, eliminating perceived input latency over high-RTT
connections (SSH, mobile, cloud IDEs).

- Zero dependencies, compatible with xterm v5.x and @xterm/xterm v5.4+
- Configurable prompt detection (character, regex, or custom function)
- Flushed text tracking for tab-switch / deferred echo scenarios
- Per-character grid-aligned rendering matching xterm's canvas output
- 56 tests passing (prompt finder, overlay renderer, full addon lifecycle)
- Dual CJS/ESM build with full TypeScript declarations

Claudeman source is unchanged — migration to consume this lib is a
separate follow-up.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/xterm-zerolag-input/package.json

@@ -0,0 +1,46 @@
+{
+  "name": "xterm-zerolag-input",
+  "version": "0.1.0",
+  "description": "Instant keystroke feedback overlay for xterm.js — eliminates perceived input latency over high-RTT connections",
+  "type": "module",
+  "main": "dist/index.cjs",
+  "module": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs"
+    }
+  },
+  "files": [
+    "dist/"
+  ],
+  "scripts": {
+    "build": "tsup src/index.ts --format cjs,esm --dts --clean",
+    "test": "vitest run",
+    "typecheck": "tsc --noEmit",
+    "prepublishOnly": "npm run build"
+  },
+  "keywords": [
+    "xterm",
+    "xterm.js",
+    "terminal",
+    "local-echo",
+    "input-latency",
+    "overlay",
+    "addon"
+  ],
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/nicobailon/claudeman",
+    "directory": "packages/xterm-zerolag-input"
+  },
+  "devDependencies": {
+    "jsdom": "^24.1.3",
+    "tsup": "^8.5.1",
+    "typescript": "^5.5.0",
+    "vitest": "^2.1.9"
+  }
+}