feat: beta features toggle + Beta pill primitive (#1829)

* feat: beta features toggle + Beta pill primitive

Adds the infrastructure for self-service beta opt-in. No call sites yet:
this PR is meant to land first so feature PRs (Goals, etc.) can ship
behind the gate incrementally.

User opts in via a single toggle at the bottom of Settings → Preferences.
The flag persists in the existing `users.preferences` JSONB column under
`beta_features_enabled` — same shape as `dashboard_two_column` and
`show_split_grouped`, so no migration is needed.

Controllers gate a beta feature by adding `before_action
:require_beta_features!` from the new `BetaGateable` concern (included in
ApplicationController). Views use the `beta_features_enabled?` helper to
hide / show nav items, banners, etc. Logged-out callers always return
false.

Ships `DS::BetaPill`, a small inline marker for tagging features as
Beta / Canary in nav, headers, and lists. Five tones (violet by default,
indigo, fuchsia, amber, gray) map to existing Sure color tokens — no raw
hex. Three styles (soft / filled / outline) and two sizes (sm / md) cover
the surfaces in the design handoff. The `dot_only:` mode renders just
the colored dot for use on a collapsed sidebar.

* review: rename to DS::Pill, fix CR/Codex nits, add tests

CodeRabbit + Codex review feedback:

- Rename DS::BetaPill → DS::Pill. The component was already generic in
  shape (tones, styles, sizes); the name was misleading scope. "Beta"
  becomes the default label (still i18n-driven). Goals' StatusPill can
  later refactor onto this primitive without a third pill.
- Localize the default pill label via i18n (`ds.pill.default_label`)
  instead of hard-coding English.
- Add role="img" to the dot-only span so the aria-label is consistently
  exposed to assistive tech.
- Wrap the Preferences toggle row in <label for="…"> so the title and
  description become an honest click target for the toggle (matches the
  cursor-pointer affordance).
- Drop arbitrary Tailwind values (py-[3px], gap-[5px], tracking-[…]) in
  favor of scale tokens. text-[10/11px] stays because the pill is
  intentionally sub-12px (Sure's smallest scale token is text-xs / 12px)
  to read as a marker, not a label.
- Add User#beta_features_enabled? predicate tests covering default-off,
  explicit-true, and non-boolean truthy values.

Won't fix:
- Palette refs (`--color-violet-*` etc.). Sure has no semantic Beta/
  Canary tokens; introducing them in this PR would be a design-system
  change beyond the scope. The component centralizes palette use in one
  `palette` method, matching the existing pattern in
  Goals::StatusPillComponent.

* review: consistent title fallback in full-pill branch

* docs: how to gate a feature behind the beta toggle

* docs: unwrap doc lines to match existing style

* chore(preview): run Cloudflare PR previews on basic instances (#1831)

* fix(preview): use Rails health endpoint for container ping (#1823)

* fix(preview): use Rails health endpoint for container ping

* fix(preview): point container ping to localhost/up

---------

Co-authored-by: Sure Admin (bot) <sure-admin@splashblot.com>

test/models/user_test.rb

@@ -660,6 +660,23 @@ class UserTest < ActiveSupport::TestCase
     assert_equal "custom_role", User.role_for_new_family_creator(fallback_role: "custom_role")
   end
 
+  # Beta features preference tests
+  test "beta_features_enabled? defaults to false" do
+    @user.update!(preferences: {})
+    assert_not @user.beta_features_enabled?
+  end
+
+  test "beta_features_enabled? true only when explicitly true" do
+    @user.update!(preferences: { "beta_features_enabled" => true })
+    assert @user.beta_features_enabled?
+
+    @user.update!(preferences: { "beta_features_enabled" => false })
+    assert_not @user.beta_features_enabled?
+
+    @user.update!(preferences: { "beta_features_enabled" => "yes" })
+    assert_not @user.beta_features_enabled?, "truthy non-boolean should not enable"
+  end
+
   # ActiveStorage attachment cleanup tests
   test "purging a user removes attached profile image" do
     user = users(:family_admin)