Feat: Add Organization Subscription-Preview Endpoint

[sbrown-livefront]

🎟️ Tracking

• PM-39928 (server subtask of PM-39927, epic PM-36631)

Stacked on PM-39925 (invoice-preview foundation). Base is billing/PM-39925/invoice-preview-projection, not main — main has none of the Bit.Invoicing / Bit.Subscriptions.Organization libraries this builds on. Review after the foundation PRs (#8208, #8209) merge.

📔 Objective

First endpoint on the new Bit.Subscriptions.Organization feature library and first consumer of the shared, Stripe-invoice-preview–driven cart summary. Sources the organization's upcoming-renewal cart totals from an actual Stripe invoice preview instead of reconstructing them from local subscription state.

Adds:

• GetSubscriptionPreviewQuery (Bit.Invoicing) — shared, ISubscriber-generic query ported from GetBitwardenSubscriptionQuery. Resolves tier/cadence (collapsing TeamsStarter → Teams), previews via create_preview(subscription=id), falls back to the subscription overload when there's no upcoming invoice, and maps subscription status → SubscriptionPreview envelope (suspension/grace-period/cancel). Registered in AddInvoicing(). The Organization path is fully wired here; the User/Premium path is stubbed for Task 8.
• GET /organizations/{organizationId:guid}/billing/subscription/preview — new route on the org subscription group, gated behind PM36631_PreviewDrivenCart.
• Authorization via AuthorizeAttribute<OrganizationBillingRequirement> using the IOrganizationRequirement framework (Owner or confirmed provider-user-for-org; excludes Admin/Custom). Lives entirely in the OrganizationAuthorization library — no dependency on the Api project.
• Unit tests for the query, the requirement, and the endpoint handler + group wiring.

Refactor (cross-cutting): AuthorizeAttribute moved into the dedicated OrganizationAuthorization library and its namespace updated. Consumers were re-pointed to the new namespace — a one-line using change across ~15 AdminConsole/Billing controllers, the PAM AccessRuleEndpoints, NoopAuthorizeAttribute, and two test files. This accounts for the otherwise-unrelated file churn; no behavior changes.

Confirmed during implementation: create_preview(subscription=id) surfaces a subscription schedule's phase-2 discount, so the legacy GetSchedulePhase2CouponIdsAsync porting was not needed.

Out of scope: Provider subscribers (ResolveTierAndCadenceAsync throws); the User/Premium route (Task 8).

📸 Screenshots

N/A — internal API endpoint, no UI in this PR.

[codecov]

Codecov Report

❌ Patch coverage is 82.69231% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.41%. Comparing base (eaeb91c) to head (ad72c4f).

Files with missing lines	Patch %	Lines
...icePreviews/Queries/GetSubscriptionPreviewQuery.cs	79.51%	13 Missing and 4 partials ⚠️
...ion/OrganizationSubscriptionEndpointsExtensions.cs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@                               Coverage Diff                               @@
##           billing/PM-39925/invoice-preview-projection    #8245      +/-   ##
===============================================================================
+ Coverage                                        63.39%   63.41%   +0.02%     
===============================================================================
  Files                                             2420     2423       +3     
  Lines                                           104400   104504     +104     
  Branches                                          9472     9483      +11     
===============================================================================
+ Hits                                             66182    66269      +87     
- Misses                                           35946    35959      +13     
- Partials                                          2272     2276       +4     

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