feat: key usage panel — display usage data for Claude, OpenCode, and Copilot

Adds 'Key Usage' to the sidebar dropdown with per-provider live usage:
- Claude: 5-hour and weekly utilization bars with reset timestamps
  (normalizes Anthropic's 0-100% API response to 0-1 internally)
- OpenCode: Scrapes usage from workspace page via OPENCODE_COOKIE
  session cookie, mapping key IDs to OPENCODE_WS1_ID/OPENCODE_WS2_ID
- Copilot: Fetches from api.github.com/copilot_internal/user with
  entitlement/remaining/quota reset tracking

New files: opencode.ts, copilot.ts (usage fetchers), KeyUsage.svelte
New route: GET /models/key-usage?keyId=X dispatches by provider

1 files changed, 64 insertions, 0 deletions

diff --git a/packages/core/src/credentials/copilot.ts b/packages/core/src/credentials/copilot.ts
new file mode 100644
index 0000000..8baf6f4
--- /dev/null
+++ b/packages/core/src/credentials/copilot.ts
@@ -0,0 +1,64 @@
+// ─── GitHub Copilot Usage Tracking ───────────────────────────
+// Uses the internal GitHub Copilot user endpoint (same one the
+// official VS Code Copilot extension calls).
+
+export interface CopilotUsageReport {
+	tokensConsumed?: number;
+	tokensRemaining?: number;
+	percentUsed?: number; // 0-100
+	resetAt?: number; // Unix timestamp ms
+	plan?: string;
+}
+
+export async function fetchCopilotUsage(
+	token: string,
+	_baseUrl: string,
+): Promise<CopilotUsageReport | null> {
+	const url = "https://api.github.com/copilot_internal/user";
+	const headers: Record<string, string> = {
+		authorization: `Bearer ${token}`,
+		accept: "application/json",
+	};
+
+	try {
+		const response = await fetch(url, { headers });
+		if (!response.ok) return null;
+
+		const data = (await response.json()) as Record<string, unknown>;
+		const plan = typeof data.copilot_plan === "string" ? data.copilot_plan : undefined;
+
+		const resetDate = typeof data.quota_reset_date === "string" ? data.quota_reset_date : undefined;
+		const resetAt = resetDate ? Date.parse(resetDate) : undefined;
+
+		const qs = data.quota_snapshots as Record<string, unknown> | undefined;
+		const pi = qs?.premium_interactions as Record<string, unknown> | undefined;
+
+		const entitlement = typeof pi?.entitlement === "number" ? pi.entitlement : undefined;
+		const remaining = typeof pi?.remaining === "number" ? pi.remaining : undefined;
+		const percentRemaining =
+			typeof pi?.percent_remaining === "number" ? pi.percent_remaining : undefined;
+
+		if (entitlement === undefined && remaining === undefined) {
+			return null;
+		}
+
+		const tokensConsumed =
+			entitlement !== undefined && remaining !== undefined ? entitlement - remaining : undefined;
+		const percentUsed =
+			percentRemaining !== undefined
+				? Math.round((100 - percentRemaining) * 100) / 100
+				: tokensConsumed !== undefined && entitlement !== undefined && entitlement > 0
+					? Math.round((tokensConsumed / entitlement) * 10000) / 100
+					: undefined;
+
+		return {
+			tokensConsumed,
+			tokensRemaining: remaining,
+			percentUsed,
+			resetAt: resetAt && !Number.isNaN(resetAt) ? resetAt : undefined,
+			plan,
+		};
+	} catch {
+		return null;
+	}
+}