feat(booth): downloadable booths — whole-booth zip + ?dl force-download (v0.1.4)

A verbatim index.html booth (e.g. edict-design-brief: a rendered brief + its
.md) had no download affordance — the page is served raw with no gallery/per-file
chrome. Adds:
  - GET /b/<name>/?download=1 -> streams the whole booth as <name>.zip (attachment)
  - GET /b/<name>/<file>?dl=1 -> forces Content-Disposition: attachment (html/md/
    text otherwise render inline with no easy save)
  - a download link on the index card (the accessible spot for verbatim booths)
    and the gallery header
Tests for both; verified live against edict-design-brief on nh3-dev :8090.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "booth"
-version = "0.1.3"
+version = "0.1.4"
 description = "The Booth — a dead-simple standing web server that scans a data dir of drop-folders and renders each as an ephemeral media 'booth' (image/webm/audio auto-gallery, or a folder's own index.html verbatim). Also accepts browser/curl uploads for pickup under a human-readable id. 24h TTL, then the folder is wiped. Fleet tool for CC sessions to surface A/B and smoke results to the operator."
 requires-python = ">=3.11"
 dependencies = [