fix(config pi): embed extension sources so installed binary is self-contained

- add scripts/generate-pi-extension.ts to embed src/pi-ext sources as
  string constants (mirrors prime-agent's embedded switcher pattern).
- config pi now writes the embedded sources by default, so it works from
  an /usr/bin install with no source tree (--extension-dir overrides for
  dev). Verified installed binary writes files byte-identical to source.
- add installEmbeddedExtension test.

src/cli/tests/utils/pi-settings.test.ts

@@ -6,6 +6,7 @@ import { agentInstallRoot } from '../../src/commands/skills.js';
 import {
   registerWithPi,
   installExtensionFiles,
+  installEmbeddedExtension,
 } from '../../src/utils/pi-settings.js';
 
 describe('skills agentInstallRoot', () => {
@@ -89,4 +90,20 @@ describe('pi-settings util', () => {
     expect(readFileSync(join(destDir, 'mcpctl-pi.ts'), 'utf-8')).toBe('// extension\n');
     expect(readFileSync(join(destDir, 'mcp-http.ts'), 'utf-8')).toBe('// client\n');
   });
+
+  it('writes the embedded extension sources (self-contained, no source tree)', async () => {
+    const destDir = join(tmp, 'embedded-ext');
+
+    const written = await installEmbeddedExtension(destDir);
+
+    expect(written).toHaveLength(2);
+    // Both filenames must be written.
+    expect(written.map((w) => w.replace(destDir + '/', ''))).toEqual(['mcpctl-pi.ts', 'mcp-http.ts']);
+    // The main file must be non-empty and import the sibling client.
+    const main = readFileSync(join(destDir, 'mcpctl-pi.ts'), 'utf-8');
+    expect(main.length).toBeGreaterThan(1000);
+    expect(main).toContain('./mcp-http.js');
+    const http = readFileSync(join(destDir, 'mcp-http.ts'), 'utf-8');
+    expect(http).toContain('McpHttpSession');
+  });
 });