init: scaffold mac project + inventory + setup design

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/reference/inventory-2026-09-15.md

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+# Mac inventory — 2026-09-15 (first SSH, pre-any-changes)
+
+Read when: deciding what to disable/install, or checking "was X already like that out of the box".
+
+## Hardware / OS
+- MacBookPro18,1 = 16" 2021, Apple M1 Pro (8P+2E), 32 GB, 512 GB SSD (425 Gi free, 14 Gi used)
+- macOS 26.2 Tahoe (build 25C56), arm64
+- Uptime 28 days at first login (used/refurb unit); 15-min load was 12.5 right after Seth's setup — settled to idle within the hour (post-setup indexing/iCloud sync, not a persistent hog)
+- Hostname: ComputerName "Seth's MacBook Pro", LocalHostName `Seths-MacBook-Pro`
+- LAN: en0 Wi-Fi 192.168.0.94. No Tailscale. Stray PPP service "SparkFun Pro Micro" (modem entry from a previously-attached USB board)
+
+## Software state (stock)
+- Shell zsh. No Homebrew, no Xcode CLT
+- /Applications: Safari + Utilities only. ~/Applications empty
+- No third-party LaunchDaemons/LaunchAgents. No user login items
+- Dock: full stock Tahoe set (Apps, Safari, Messages, Mail, Maps, Photos, FaceTime, Phone, Calendar, Contacts, Reminders, Notes, TV, Music, Games, App Store, iPhone Mirroring, System Settings, Terminal)
+
+## Services / security
+- Siri: off (`Assistant Enabled = 0`). Apple Intelligence: opted out at Setup Assistant (`opted_out_buddy = 1`)
+- iCloud: 1 account signed in
+- Spotlight: indexing enabled on /
+- Time Machine: no destinations
+- SIP enabled, Gatekeeper enabled, **FileVault ON** (=> after a reboot, SSH is unreachable until someone types the password at the lid; plan remote work accordingly)
+- Remote Login: enabled by Seth 2026-09-15; claude@steel141 ed25519 key installed in ~/.ssh/authorized_keys
+- Screen Sharing: not running
+- pmset: sleep 1 / displaysleep 10 / disksleep 10 / powernap 1 / hibernatemode 3 / lowpowermode 0
+
+## Audio
+- Built-in mic + speakers only. No interface attached at inventory time