feat: wire shared/github-auth.sh into all agent flows (#1216)

* feat: wire shared/github-auth.sh into all agent flows

Add offer_github_auth() to shared/common.sh and call it from the
inject_env_vars_* functions so all agent flows automatically offer
GitHub CLI setup after env var injection — no per-script changes needed.

Changes:
- shared/common.sh: add offer_github_auth() function, call it from
  inject_env_vars_ssh() and inject_env_vars_local()
- sprite/lib/common.sh: call offer_github_auth() from
  inject_env_vars_sprite()
- OVH is covered automatically (inject_env_vars_ovh delegates to
  inject_env_vars_ssh)

Behavior:
- Prompts "Set up GitHub CLI (gh) on this machine? (y/N):"
- Defaults to No (non-blocking for users who don't need it)
- Skippable via SPAWN_SKIP_GITHUB_AUTH=1 env var for CI/automation
- Uses safe_read for curl|bash compatibility
- Downloads and runs shared/github-auth.sh on the remote VM

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: add shared agent setup helpers, deduplicate hetzner scripts (#1236)

Add 5 composable helper functions to shared/common.sh (install_agent,
verify_agent, get_or_prompt_api_key, inject_env_vars_cb, launch_session)
that use the same callback pattern as offer_github_auth and
setup_claude_code_config. Refactor all 15 hetzner agent scripts to use
them, reducing total line count from 868 to 579 (-33%).

Phase 1 of multi-phase rollout — remaining clouds to follow.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hetzner/opencode.sh

@@ -12,35 +12,22 @@ fi
 log_info "OpenCode on Hetzner Cloud"
 echo ""
 
+# Provision server
 ensure_hcloud_token
 ensure_ssh_key
-
 SERVER_NAME=$(get_server_name)
 create_server "${SERVER_NAME}"
 verify_server_connectivity "${HETZNER_SERVER_IP}"
 wait_for_cloud_init "${HETZNER_SERVER_IP}" 60
 
-log_step "Installing OpenCode..."
-run_server "${HETZNER_SERVER_IP}" "$(opencode_install_cmd)"
-log_info "OpenCode installed"
+# Set up callbacks
+RUN="run_server ${HETZNER_SERVER_IP}"
+UPLOAD="upload_file ${HETZNER_SERVER_IP}"
+SESSION="interactive_session ${HETZNER_SERVER_IP}"
 
-echo ""
-if [[ -n "${OPENROUTER_API_KEY:-}" ]]; then
-    log_info "Using OpenRouter API key from environment"
-else
-    OPENROUTER_API_KEY=$(get_openrouter_api_key_oauth 5180)
-fi
-
-log_step "Setting up environment variables..."
-inject_env_vars_ssh "${HETZNER_SERVER_IP}" upload_file run_server \
+# Install, configure, launch
+install_agent "OpenCode" "$(opencode_install_cmd)" "$RUN"
+get_or_prompt_api_key
+inject_env_vars_cb "$RUN" "$UPLOAD" \
     "OPENROUTER_API_KEY=${OPENROUTER_API_KEY}"
-
-echo ""
-log_info "Hetzner server setup completed successfully!"
-log_info "Server: ${SERVER_NAME} (ID: ${HETZNER_SERVER_ID}, IP: ${HETZNER_SERVER_IP})"
-echo ""
-
-log_step "Starting OpenCode..."
-sleep 1
-clear
-interactive_session "${HETZNER_SERVER_IP}" "source ~/.zshrc && opencode"
+launch_session "Hetzner server" "$SESSION" "source ~/.zshrc && opencode"