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, 19 insertions, 10 deletions

diff --git a/packages/core/src/credentials/index.ts b/packages/core/src/credentials/index.ts
index d72ad48..0ae4edb 100644
--- a/packages/core/src/credentials/index.ts
+++ b/packages/core/src/credentials/index.ts
@@ -1,18 +1,27 @@
 export {
-	type ClaudeCredentials,
+	ANTHROPIC_MODELS_FALLBACK,
+	buildBillingHeaderValue,
 	type ClaudeAccount,
+	type ClaudeCredentials,
+	type ClaudeProfile,
 	type ClaudeUsageBucket,
 	type ClaudeUsageReport,
-	type ClaudeProfile,
-	ANTHROPIC_MODELS_FALLBACK,
-	fetchAnthropicModels,
 	discoverClaudeAccounts,
-	refreshAccountCredentials,
-	refreshAccountCredentialsAsync,
-	validateAccountCredentials,
-	buildBillingHeaderValue,
+	fetchAnthropicModels,
+	getAccountUsage,
 	getAnthropicBetas,
 	getAnthropicHeaders,
-	getAccountUsage,
+	refreshAccountCredentials,
+	refreshAccountCredentialsAsync,
 	SYSTEM_IDENTITY,
-} from "./claude.js";
\ No newline at end of file
+	validateAccountCredentials,
+} from "./claude.js";
+export {
+	type CopilotUsageReport,
+	fetchCopilotUsage,
+} from "./copilot.js";
+export {
+	fetchOpencodeUsage,
+	type OpencodeUsageBucket,
+	type OpencodeUsageReport,
+} from "./opencode.js";