feat: GitHub provider lifecycle and onboarding hardening (#351)

* feat: improve GitHub provider onboarding and lifecycle

* fix: address copilot review in provider manager

* fix: address follow-up copilot review comments

* test: resolve rebase conflict in provider profiles suite

* fix: clear stale github hydrated marker

* fix: harden github onboarding auth precedence

* fix: remove merge markers from provider tests

* fix: resolve latest copilot onboarding comments

---------

Co-authored-by: KRATOS <84986124+gnanam1990@users.noreply.github.com>

src/utils/providerProfile.test.ts

@@ -485,6 +485,26 @@ test('buildStartupEnvFromProfile leaves explicit provider selections untouched',
   assert.equal(env.OPENAI_API_KEY, undefined)
 })
 
+test('buildStartupEnvFromProfile leaves profile-managed env untouched', async () => {
+  const processEnv = {
+    CLAUDE_CODE_PROVIDER_PROFILE_ENV_APPLIED: '1',
+    ANTHROPIC_BASE_URL: 'https://api.anthropic.com',
+    ANTHROPIC_MODEL: 'claude-sonnet-4-6',
+  }
+
+  const env = await buildStartupEnvFromProfile({
+    persisted: profile('openai', {
+      OPENAI_API_KEY: 'sk-persisted',
+      OPENAI_MODEL: 'gpt-4o',
+    }),
+    processEnv,
+  })
+
+  assert.equal(env, processEnv)
+  assert.equal(env.ANTHROPIC_MODEL, 'claude-sonnet-4-6')
+  assert.equal(env.OPENAI_MODEL, undefined)
+})
+
 test('buildStartupEnvFromProfile treats explicit falsey provider flags as user intent', async () => {
   const processEnv = {
     CLAUDE_CODE_USE_OPENAI: '0',