refactor(cli): migrate to commander framework and simplify config loading

Replace hand-rolled CLI argument parsing with Commander for command
registration and option handling. Streamline config resolution by
removing the BrickConfig type and accepting a plain source string
with BRICK_SOURCE env var support.

- Replace manual CLI dispatch with Commander-based command tree
- Simplify resolveConfig/resolveSource to a single resolveSource function
- Remove BrickConfig interface in favor of direct source string
- Move isRemote check into index-loader as a local utility
- Update loadIndex signature to accept source string directly

src/lib/config.ts

@@ -1,30 +1,8 @@
-import type { BrickConfig } from "../types/index.js";
-
 const DEFAULT_SOURCE =
   "https://gitea.synoth.com/synoth/brick-index/raw/branch/master/blocks.yaml";
 
-function parseSourceFromArgs(args: string[]): string | undefined {
-  const idx = args.indexOf("--source");
-  if (idx !== -1 && idx + 1 < args.length) {
-    return args[idx + 1];
-  }
-  return undefined;
-}
-
-function isRemoteSource(source: string): boolean {
-  return source.startsWith("http://") || source.startsWith("https://");
-}
-
-export function resolveConfig(args: string[]): BrickConfig {
-  const cliSource = parseSourceFromArgs(args);
-  if (cliSource) {
-    return { source: cliSource, isRemote: isRemoteSource(cliSource) };
-  }
-
-  const envSource = process.env.BRICK_SOURCE;
-  if (envSource) {
-    return { source: envSource, isRemote: isRemoteSource(envSource) };
-  }
-
-  return { source: DEFAULT_SOURCE, isRemote: true };
+export function resolveSource(cliSource?: string): string {
+  if (cliSource) return cliSource;
+  if (process.env.BRICK_SOURCE) return process.env.BRICK_SOURCE;
+  return DEFAULT_SOURCE;
 }