fix(terminal): Claude panes scroll 5 lines per wheel notch

Fullscreen Claude Code scrolls one line per wheel report when its terminal
does not answer XTVERSION as xterm.js (behind tmux it never does), and
xterm.js sends one report per notch — so a notch moved a single line.
spawnRun now sets CLAUDE_CODE_SCROLL_SPEED=5 unless the dashboard's env
already sets it; settings.json env and /config Scroll speed still win.

server/__tests__/lane-sources.test.js

@@ -208,6 +208,9 @@ describe("lane-sources instructions and launch", () => {
     // Claude Code hides its task tools from newer models without this, and the
     // chat Progress panel is drawn from those calls.
     assert.ok(newSession.includes("CLAUDE_CODE_ENABLE_TODO_TOOLS=1"));
+    // One wheel notch reaches claude as one report; it scrolls this many lines.
+    if (!process.env.CLAUDE_CODE_SCROLL_SPEED)
+      assert.ok(newSession.includes("CLAUDE_CODE_SCROLL_SPEED=5"));
     assert.deepEqual(fs.readdirSync(dir), ["CLAUDE.md"]);
     const text = fs.readFileSync(path.join(dir, "CLAUDE.md"), "utf8");
     assert.match(text, /^- always answer in Vietnamese/);