fix: address code review findings across WS, CJK input, install.sh, and README

WebSocket route: add socket error handler to prevent process crashes, enforce
per-session connection limit (max 5), track/decrement counts on close.

CJK input: add destroy() method with proper listener cleanup, guard against
double-init, add maxlength/aria-label to textarea, use language-neutral
placeholder, explicitly clear cjkActive on hide.

install.sh: fix update() to use $BRANCH and $REPO_URL instead of hardcoded
origin/master — fork users were silently switched back to master on update.

README: fix broken markdown table (paragraph concatenated into last cell),
add CODEMAN_NODE_VERSION to env var table.

Tests: add 8 new test cases for batch coalescing, flush threshold, unknown
message types, connection limit, heartbeat, readyState guards. Import
MAX_INPUT_LENGTH from config, add connectWs timeout, replace setTimeout
with vi.waitFor in cleanup test.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/web/public/index.html

@@ -233,7 +233,8 @@
     <main class="main">
       <div class="terminal-wrap">
         <div class="terminal-container" id="terminalContainer"></div>
-        <textarea id="cjkInput" rows="1" placeholder="CJK 입력 → Enter 전송 / ESC 취소"
+        <textarea id="cjkInput" rows="1" placeholder="CJK input (Enter = send, Esc = clear)"
+          maxlength="65536" aria-label="CJK IME input field"
           autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"></textarea>
       </div>