workstation: standardize on the native claude install (drop npm-global + npx)

Question from Viktor: should claude run via the binary or npx? Answer: the native
install is the recommended runtime (self-contained, self-updating ~/.local/bin/claude;
installMethod=native) — and every existing user had already auto-migrated to it, leaving
the npm-global copy empty and the npx fallback dead. "Leave only the recommended setup":

- setup-devvm.sh: node is now installed ONLY for the t3 CLI; dropped the machine-wide
  `npm install -g @anthropic-ai/claude-code` (npm/npx is not the recommended runtime and
  just shadowed the per-user native installs).
- t3-provision-users.sh: new per-user `install_user_claude_native` (runs the official
  https://claude.ai/install.sh AS the user, idempotent/skip-if-present) — provisions native
  claude for BOTH the terminal launcher and each t3-serve instance, replacing the npm bootstrap.
- skel/start-claude.sh: launcher runs the native `claude` only; if missing it bootstraps via
  the native installer (was an `npx @anthropic-ai/claude-code` fallback).
- docs/architecture/multi-tenancy.md: documented the native-only runtime model.

node stays (the pinned t3 CLI is npm-global). Verified: native installer reachable +
produces ~/.local/bin/claude 2.1.177; all three scripts pass bash -n + shellcheck.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/workstation/skel/start-claude.sh

@@ -42,13 +42,16 @@ else
   done
 fi
 
-# Prefer the system-wide `claude` (installed by setup-devvm.sh); fall back to npx.
+# Run the NATIVE `claude` (the recommended install: ~/.local/bin/claude, self-updating).
+# No npm/npx. If the native binary is missing (a fresh account before the hourly reconcile
+# has provisioned it), bootstrap it with the official native installer, then run it.
 launch() {
-  if command -v claude >/dev/null 2>&1; then
-    claude "$@"
-  else
-    npx @anthropic-ai/claude-code "$@"
+  if ! command -v claude >/dev/null 2>&1; then
+    echo "  Installing Claude Code (native) for $(id -un) …"
+    curl -fsSL https://claude.ai/install.sh | bash || return 127
+    export PATH="$HOME/.local/bin:$PATH"
   fi
+  claude "$@"
 }
 
 # Re-assert Claude Code's first-run onboarding flag before launch. ~/.claude.json is a