move host setup into scripts/setup/

scripts/ was holding two unrelated kinds of thing: install-this-machine, and run-this-occasionally. The
eight installers now live in scripts/setup/; what stays at the top level is the build steps (gen-index,
prebuild, build/) and the two maintenance scripts (reindex-music, rebuild-soulseek-tree).

The move is not just a rename. Three of these derive the repo root from their own location:

  setup.sh:51            PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
  setup_mac_light.sh:51  same
  cleanup-desktop.sh:134 ENV_FILE="$(dirname "$0")/../.env"

Left alone, all three would now resolve to scripts/ — and nothing downstream complains. PROJECT_DIR is
where .env is written, where `bun install`, `gen:index` and `db:push` run, and what pm2 is pointed at, so
a fresh install would have quietly provisioned scripts/ and reported success. cleanup-desktop.sh fails
the other way: it would find no .env, print "No .env — skipping", and leave the real VNC_PASSWORD in the
real file. All three are now `../..` with a comment saying why the level matters.

provision-user-dirs.ts imports data-path.ts relatively; that one tsgo caught.

Also disambiguated `setup.sh` where it had become two files. app-store/templates/<name>/setup.sh is a
per-sidecar installer with its own contract, and preflight.ts + docs/sidecar-app-store.md discussed both
in the same paragraph. The host one is now spelled with its full path at those sites.

Verified: bash -n on all six shell scripts, tsgo clean, os-user tests pass, both derivations resolve to
the repo root, starship.toml still resolves from os-user-shell.ts, and provision-user-dirs.ts runs under
DRY_RUN.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

TODO.md

@@ -52,7 +52,7 @@ the owner's OS user and can never be granted. Indirection there really is accide
       `'Unverified'` and `signin.ts` refuses anything else with a bare UNAUTHORIZED, which is the trap
       the hand-INSERT route fell into. The owner sets the password and reads it out; `passwordChangedAt`
       stays null. Directories come from the shared `provisionUserDirs`/`USER_DIRS` in `data-path.ts`,
-      which `scripts/provision-user-dirs.ts` now imports rather than restating.
+      which `scripts/setup/provision-user-dirs.ts` now imports rather than restating.
 
 - [ ] **Still no invite flow, and no password reset for a member.** The owner types the password and
       tells the person, which means the owner knows it and the member cannot change it back if they