v1.1.0 — Layout + spaces toolbar, one-command setup

Second release. Adds the spaces-toolbar theming and turns setup into a single
command.

Theme (CSS)

• Spaces toolbar: light rail, vertically-centred + slightly smaller icons.
• Folder pane: hidden header bar; toned section divider; symmetric spacing.
• Message header: hide noisy technical rows (message-id, references, list-*, …).

One-command setup

• deploy.ps1 now applies CSS + recommended prefs (user.js) + recommended
  layout (xulstore.json) in one go (layout only when Betterbird is closed).
  -SkipPrefs / -SkipLayout to opt out.
• New configure-prefs.ps1 (Vertical layout, Cards view, 2-line cards,
  icon-over-text toolbar, threaded, …) and configure-xulstore.ps1 (clean mail
  toolbar, Unified Folders + All + Tags, menu auto-hide, quick-filter hidden,
  compact header).

See CHANGELOG.md for details. Targets Betterbird 140.12.0esr-bb24.

v1.0.0 — Postbox "Monterail Dark" for Betterbird 140

First complete release. A pure userChrome/userContent CSS recreation of
Postbox's Monterail Dark look on Betterbird 140.12.0esr-bb24.

Themes the thread pane, folder pane, toolbar, tabs, message header, composer,
status bar, and the email body. All design values are --pb-* tokens in
chrome/postbird/config.css; every rule is mapped in docs/selector-map.md for
cheap repair after ESR bumps.

Install: clone → ./scripts/deploy.ps1 → enable
toolkit.legacyUserProfileCustomizations.stylesheets, switch to Cards view,
restart. See the README and CHANGELOG.md for details and known limitations.