chore(core): remove orphan PageTabs + clean post-i18n doc drift (#4192)

* chore(core): remove orphan PageTabs + clean post-i18n doc drift

- delete core.pageTabs.component.{vue,test} (zero consumers since SurfaceTabBar)
- MIGRATIONS.md: remove dangling src/lib/plugins/i18n.js reference; add PageTabs drop note
- billing.static-content.js: fix 3 stale "fallback to i18n keys" comments

Closes audit P1 (2026-05-21).

* docs(billing): fix MIGRATIONS component name + static-content JSDoc accuracy (CR)

- MIGRATIONS.md: replace SurfaceTabBar → CoreSurfaceTabBar, make downstream
  deletion paths explicit (vue + test file separately)
- static-content.js faqs @type: add string|null to subtitle, describe falsy fallback
- static-content.js tabs: clarify two-layer fallback (devkit default 'Extras'
  vs view hardcoded 'Units' when field absent/falsy)
- static-content.js header: wording updated to 'any falsy value (including
  empty string) triggers view fallback'

Author: PierreBrisorgueil

MIGRATIONS.md

@@ -266,6 +266,18 @@ This migration is **opt-in per module** — coordinate with the maintainer of ea
 
 ---
 
+## Drop CorePageTabsComponent (2026-05-21)
+
+The `core.pageTabs.component.vue` introduced in PR #4183 was abandoned 2h after merge in favor of `CoreSurfaceTabBar` (PR #4187). The component had zero consumers and is removed.
+
+**Downstream action:** if you propagated the files via `/update-stack`, delete both:
+- `src/modules/core/components/core.pageTabs.component.vue`
+- `src/modules/core/tests/core.pageTabs.component.unit.tests.js`
+
+Use `CoreSurfaceTabBar` (`core.surfaceTabBar.component.vue`) for any tab layouts.
+
+---
+
 ## Legal module + cookie consent banner (2026-05-07)
 
 **Non-breaking for default consumers.** New `modules/legal/` ships:
@@ -285,7 +297,7 @@ Disabled by default. Enable in `modules/legal/config/legal.{env}.config.js` (or
 - MODIFIED: `src/modules/core/components/core.footer.component.vue` — auto-injects a "Legal" section when `legal.cookieConsent.enabled` or any `legal.pages.items[*].enabled` is true. Also fixes a pre-existing bug where the footer was hidden on hard-load (the `$route` watcher didn't fire on initial mount); a `created()` hook now initializes `enabled` from `$route.meta.footer`.
 - MODIFIED: `src/modules/app/app.vue` — global mount of `<legalCookieBanner />`.
 - MODIFIED: `src/modules/app/app.router.js` — concatenates legal routes (returns empty when `pages.enabled: false`).
-- MODIFIED: `src/lib/plugins/i18n.js` — imports `legalEn` / `legalFr`.
+- ~~MODIFIED: `src/lib/plugins/i18n.js` — imports `legalEn` / `legalFr`.~~ **Superseded:** `src/lib/plugins/i18n.js` was removed entirely in PR #4169 (i18n removal). Legal strings are now hardcoded in English directly in the legal components.
 
 ### Action for downstream projects
 

src/modules/billing/config/billing.static-content.js

@@ -163,8 +163,10 @@ export const packs = [
 ];
 
 /**
- * @desc FAQ section content. Title + subtitle are optional (fallback to i18n).
- * @type {{ title?: string, subtitle?: string, content: Array<{id: string, question: string, answer: string}> }}
+ * @desc FAQ section content. `title` and `subtitle` are optional; any falsy value (including
+ * `null` or empty string) triggers the view's hardcoded fallback:
+ * `'Frequently asked questions'` for title, `null` (no subtitle rendered) for subtitle.
+ * @type {{ title?: string|null, subtitle?: string|null, content: Array<{id: string, question: string, answer: string}> }}
  */
 export const faqs = {
   title: 'Frequently asked questions',
@@ -190,9 +192,10 @@ export const faqs = {
 
 /**
  * @desc Configurable tab labels (used in 'both-tabs' mode).
- * Each field is optional — when omitted the view falls back to i18n keys
- * `billing.pricing.tabs.plans` / `billing.pricing.tabs.units`.
+ * This devkit default ships `plans: 'Plans'` / `units: 'Extras'`.
  * Downstream projects can override either or both labels per project.
+ * The view's hardcoded fallback (`'Plans'` / `'Units'`) only applies when
+ * the field is entirely absent or falsy — it is not reached under the devkit default.
  * @type {{ plans?: string, units?: string }}
  */
 export const tabs = {
@@ -201,8 +204,9 @@ export const tabs = {
 };
 
 /**
- * @desc Page header copy. When `null`/absent, falls back to i18n keys
- * `billing.pricing.title` / `billing.pricing.subtitle`.
+ * @desc Page header copy. Any falsy value (including `null`, `undefined`, or empty string)
+ * triggers the view's hardcoded English fallback
+ * (`'Pricing'` / `'Choose the plan that fits your needs.'`).
  * @type {{ title?: string|null, subtitle?: string|null }}
  */
 export const header = {