tool registry, claude tool awareness, and model selector fix

- Add agent-agnostic tool registry (tool-registry.ts) that discovers tools from disk
- Embed tool-loader extension as platform infrastructure (ensure-tool-loader.ts)
- Inject tool context into Claude prompts on first message
- Add marketplace tool sync (sync-marketplace.ts)
- Fix model selector defaulting to claude-code when no model explicitly selected
- Exclude tool-loader-source.ts from tsconfig (Pi-specific deps)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/servers/ensure-tool-loader.ts

@@ -0,0 +1,17 @@
+import { mkdirSync, readFileSync, writeFileSync } from 'node:fs';
+import { join, resolve } from 'node:path';
+import { DATA_PATH } from './data-path';
+
+const SOURCE_PATH = resolve(import.meta.dir, 'tool-loader-source.ts');
+
+export function ensureToolLoader(): void {
+  const targetDir = join(DATA_PATH, 'extensions', 'tool-loader');
+  const targetFile = join(targetDir, 'index.ts');
+
+  mkdirSync(targetDir, { recursive: true });
+
+  const source = readFileSync(SOURCE_PATH, 'utf-8');
+  writeFileSync(targetFile, source, 'utf-8');
+
+  console.log('[bootstrap] Wrote tool-loader extension →', targetFile);
+}