Content sprint, billing UX, and weekend fixes

Three blog posts + landing refactor (4/20)

Pushed three new pieces to the blog: Integration deep-dive (PR https://github.com/deariary/blog/pull/129 targeting "linear journal" — 90/mo, +57%), Five Minute Journal hidden costs (PR https://github.com/deariary/blog/pull/130 targeting "five minute journal" — 6,600/mo, -46%), and a Proust’s madeleine evidence essay (targets "proust madeleine" — 4,400/mo). Also aligned the landing page layout to the design handoff while keeping Astro, i18n, and SEO wiring intact (LP PR https://github.com/deariary/lp/pull/203).

Logged JRNL-812: billing summary on plan change (4/21)

Opened JRNL-812 to replace the generic confirm dialog with a proper billing summary that spells out what changes, when they take effect, and any proration — link: https://linear.app/unhappychoice/issue/JRNL-812/featbilling-replace-confirm-dialog-with-a-billing-summary-on-plan. The current flow is a one-liner ("{plan}にアップグレードします。Stripeの決済画面に移動します。") so this ticket is explicitly about clarity for upgrades/downgrades/period switches/resumes/cancels.

Weekend dependency sweep, CVE fix, and CI OOM tweak (4/25)

Bumped Ruby deps (parallel → 2.1.0, rubocop → 1.86.1) across irasutoya-tools/irasutoya, irasutoya-tools/irasutoya-cli, circleci-tools/circleci-cli, bitflyer-tools/bitflyer, and bitflyer-tools/bitflyer-cli to unblock Dependabot, forced tar@^7.x via overrides to clear a CVE (merged cycle-flyer PR https://github.com/bitflyer-tools/cycle-flyer/pull/872), and fixed an Android deploy OOM by bumping CircleCI resource_class to large and tuning JVM/Gradle (merged DroidFlyer PR https://github.com/bitflyer-tools/DroidFlyer/pull/510).