feat(api): Extend license check response to distinguish trial / paid / expired paid status

[Devsome]

The current license validation endpoint returns only a boolean (valid). The silkpanel‑cms hard‑lock feature needs more granular information to decide whether to show a permanent lockout (paid license expired) or simply restrict updates (trial expired). The API must be extended to return:

• status: string enum with values active_paid, expired_paid, trial, expired_trial, never_paid (or similar).
• has_ever_paid: boolean – indicates if the user has at least one completed Stripe payment or a Stripe customer ID exists.
• plan_tier: optional string (e.g., basic, pro) – for future feature flag usage.
• expires_at: ISO 8601 date/time string – when the current paid period ends (null if never paid).
• grace_period_days: integer – remaining days until hard lock if license expired (optional, could be calculated on CMS side).

Acceptance criteria for devso.me:

• The license check endpoint returns the new fields alongside valid.
• The logic to determine has_ever_paid is based on the existence of a Stripe customer ID linked to the user account and/or a successful payment history (at least one paid invoice).
• A user who only ever used a trial returns has_ever_paid: false and status: trial or expired_trial.
• A user whose paid subscription has expired returns has_ever_paid: true, status: expired_paid.
• An active paid user returns status: active_paid.
• The new response is backward‑compatible – existing CMS versions ignoring the extra fields must continue to work (the valid field remains the primary signal).
• The implementation does not break any existing client relying on the old response format (additive change only).

Out of scope for devso.me sub‑ticket:

• Changes to the purchasing flow or Stripe integration itself.
• Returning full payment history – only the derived status flags are needed.
• Any rate‑limiting changes (should be handled separately if required).

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Acceptance criteria (main CMS ticket)

• A paid license that expires causes the entire Filament admin panel to become inaccessible behind a permanent, non‑dismissable modal.
• The lock takes effect on the next admin page load after the license is detected as expired.
• Trial license expiration does not trigger this lock; trial behavior remains unchanged.
• No admin route can bypass the modal – the middleware covers all registered admin paths.
• The enforcement mechanism is delivered as the separate silkpanel/license-enforcement package.
• Documentation is updated to reflect the new locking behavior and the difference between trial and paid license expiration.
• A grace period for unreachable license servers prevents false lockouts (configurable).
• There is no built‑in “super admin bypass” – support intervention requires direct server access.

Out of scope

• Renewal or payment UI inside the CMS (all handled on devso.me).
• Locking the public frontend – only the admin panel is affected.
• Feature‑specific partial locks (e.g., keeping some pages accessible) – the entire panel is blocked.
• Detailed design of the modal beyond the basic permanent overlay and message.