Add Pulumi for tailnet IaC management (#15)

## Summary
- Manage tail8d86e.ts.net ACLs, tags, and DNS via Pulumi + Python
- State stored in Pulumi Cloud (free tier) to avoid circular dependency
- OAuth authentication via 1Password for secure credential management
- New mise tasks: `tailnet-preview`, `tailnet-up`

## Architecture
Two-layer approach:
- **Layer 1 (Pulumi)**: Tailnet-wide config (ACLs, tags, DNS)
- **Layer 2 (Ansible)**: Node-local `tailscale serve` config (unchanged)

## Test plan
- [x] Exported current ACL from Tailscale API
- [x] Imported existing ACL into Pulumi state
- [x] Verified `mise run tailnet-preview` shows no changes
- [x] Verified `mise run tailnet-up` applies successfully

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.tail8d86e.ts.net/eblume/blumeops/pulls/15

mise-tasks/tailnet-up

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+#MISE description="Apply tailnet changes with Pulumi"
+
+set -euo pipefail
+
+export TAILSCALE_OAUTH_CLIENT_ID=$(op --vault vg6xf6vvfmoh5hqjjhlhbeoaie item get wi6bkf7bcccwfy4eu776ab4p4u --fields client_id)
+export TAILSCALE_OAUTH_CLIENT_SECRET=$(op --vault vg6xf6vvfmoh5hqjjhlhbeoaie item get wi6bkf7bcccwfy4eu776ab4p4u --fields client_secret --reveal)
+export TAILSCALE_TAILNET="tail8d86e.ts.net"
+
+cd "$(dirname "$0")/../pulumi"
+pulumi up "$@"