docs: make telemetry section collapsible and concise

Introduces privacy-first usage analytics to help understand how OpenSpec
is being used. Key privacy protections:

- Only tracks command names and version (no arguments, paths, or content)
- Opt-out via OPENSPEC_TELEMETRY=0 or DO_NOT_TRACK=1
- Auto-disabled in CI environments
- No IP address collection (explicitly disabled)
- Anonymous ID is a random UUID with no PII

Uses PostHog with a reverse proxy to avoid ad blockers. First-run shows
a one-line notice informing users about the collection.

src/cli/index.ts

@@ -50,10 +50,7 @@ program
 program.option('--no-color', 'Disable color output');
 
 // Apply global flags and telemetry before any command runs
-// Note: preAction receives (thisCommand, actionCommand) where:
-// - thisCommand: the command where hook was added (root program)
-// - actionCommand: the command actually being executed (subcommand)
-program.hook('preAction', async (thisCommand, actionCommand) => {
+program.hook('preAction', async (thisCommand) => {
   const opts = thisCommand.opts();
   if (opts.color === false) {
     process.env.NO_COLOR = '1';
@@ -62,8 +59,8 @@ program.hook('preAction', async (thisCommand, actionCommand) => {
   // Show first-run telemetry notice (if not seen)
   await maybeShowTelemetryNotice();
 
-  // Track command execution (use actionCommand to get the actual subcommand)
-  const commandPath = getCommandPath(actionCommand);
+  // Track command execution
+  const commandPath = getCommandPath(thisCommand);
   await trackCommand(commandPath, version);
 });
 

test/telemetry/config.test.ts

@@ -14,25 +14,20 @@ import {
 describe('telemetry/config', () => {
   let tempDir: string;
   let originalHome: string | undefined;
-  let originalUserProfile: string | undefined;
 
   beforeEach(() => {
     // Create temp directory for tests
     tempDir = path.join(os.tmpdir(), `openspec-telemetry-test-${Date.now()}`);
     fs.mkdirSync(tempDir, { recursive: true });
 
-    // Mock HOME/USERPROFILE to point to temp dir
-    // On POSIX, os.homedir() uses HOME; on Windows it uses USERPROFILE
+    // Mock HOME to point to temp dir
     originalHome = process.env.HOME;
-    originalUserProfile = process.env.USERPROFILE;
     process.env.HOME = tempDir;
-    process.env.USERPROFILE = tempDir;
   });
 
   afterEach(() => {
-    // Restore HOME/USERPROFILE
+    // Restore HOME
     process.env.HOME = originalHome;
-    process.env.USERPROFILE = originalUserProfile;
 
     // Clean up temp directory
     fs.rmSync(tempDir, { recursive: true, force: true });