…mon code

Replace the duplicated shared utility/validation/crypto/geo/dynamic-LINQ/
ASP.NET code in Common/ with references to the published packages
OpenShock.Internal.Common, OpenShock.Internal.AspNet and
OpenShock.Internal.DynamicLinq (pinned at 0.0.1).

- Delete 38 now-redundant files (exact duplicates + the PasswordHashingAlgorithm
  enum + the Cloudflare IP generation, now owned by the package).
- Re-point ~150 consumers to the OpenShock.Internal.* namespaces.
- OpenShockControllerBase now inherits the package base, keeping API-specific
  session/cookie/legacy-response helpers.
- Split HardLimits: shared limits come from the package, API-specific extras
  move to a new local ApiHardLimits.
- Split IQueryableExtensions: ApplyFilter/ApplyOrderBy from the package,
  WhereUserIdMatches/WhereIsUserOrPrivileged stay local.
- Adapt to package surface changes: CryptoUtils.RandomString rename,
  OpenShockProblem.WriteAsJsonAsync / OpenShockExceptionHandler now take
  JsonSerializerOptions (registered JsonOptions.Default in DI), ApplyOrderBy
  is now static.
- Bump BCrypt.Net-Next 4.2.0 -> 4.2.1 (required by OpenShock.Internal.Common).
- Drop the 6 Common.Tests files now covered by the packages' own test projects.