fix(ui): keep the plan-usage chip's 5h slot when no session window is open

The header chip silently shrank from "5h 4% · 7d 52%" to a lone "7d 52%", which
reads as half the feature breaking rather than as an idle window.

Nothing was broken. Claude Code documents `rate_limits.five_hour` as "present
only while the API reports it and its resets_at has not passed", so between
5-hour session windows the key simply leaves the statusline payload. Codeman's
snapshot replaces the Claude half wholesale on every sample, so the segment
disappeared until usage opened a new window. Confirmed against a live 2.1.252
session by capturing real statusline payloads on an isolated tmux socket: the
boot render carries no `rate_limits` at all, and the first post-response render
carries both windows.

The slot now stays, with a dimmed em dash. Claude only: a missing CODEX bucket
means that plan has no such limit rather than an idle window, so those stay
omitted (pinned by the existing test). The placeholder can never stand alone
either — hasWindows() still gates the row, so a provider reporting nothing
renders nothing rather than a row of dashes. The tooltip says "5-hour limit: no
active session window" instead of dropping the line.

Verified in a real browser against a dev instance: the idle chip renders
"5h — · 7d 52%" with the dash at opacity 0.55 in --text-dim while the live
value keeps its green, and the chip holds its shape (100px idle vs 107px with
both windows).

test/plan-usage-chip.test.ts

@@ -80,6 +80,34 @@ describe('header plan usage chip', () => {
     expect(codexRow).toContain('7d');
   });
 
+  it("keeps Claude's 5h slot as a dash when no session window is open", () => {
+    // Claude Code ships `five_hour` "only while the API reports it and its
+    // resets_at has not passed", so between session windows the key is simply
+    // absent. The chip used to shrink to a lone 7d segment, which reads as a
+    // broken feature rather than an idle window (reported 2026-09-01).
+    const { CodemanApp, chip } = loadCodemanAppClass();
+    const app = Object.create((CodemanApp as { prototype: object }).prototype) as UsageApp;
+
+    app.updatePlanUsageChip({ sevenDay: { usedPercentage: 52, resetAt: 2000 } });
+
+    expect(chip.innerHTML).toContain('pu-win-idle');
+    expect(chip.innerHTML).toContain('5h');
+    expect(chip.innerHTML).toContain('52%');
+    expect(chip.title).toContain('no active session window');
+  });
+
+  it('renders no row at all for a provider reporting nothing', () => {
+    // The placeholder must never stand alone: a row of em dashes would claim a
+    // provider is idle when it is really absent.
+    const { CodemanApp, chip } = loadCodemanAppClass();
+    const app = Object.create((CodemanApp as { prototype: object }).prototype) as UsageApp;
+
+    app.updatePlanUsageChip({ codex: { sevenDay: { usedPercentage: 40, resetAt: 3000 } } });
+
+    expect(chip.innerHTML).not.toContain('pu-win-idle');
+    expect(chip.innerHTML).toContain('40%');
+  });
+
   it('drops the provider label when Claude is the only provider with limits', () => {
     const { CodemanApp, chip } = loadCodemanAppClass();
     const app = Object.create((CodemanApp as { prototype: object }).prototype) as UsageApp;