Upgrade PHPStan to 2.x and raise analysis level from 6 to 10

- Bump phpstan/phpstan ^2.0 and szepeviktor/phpstan-wordpress ^2.0
- Move the analysis level into phpstan.neon (single source) and raise it to 10
- Add Val, a runtime coercion helper that narrows untyped WordPress boundary
  values (wpdb rows, REST params, superglobals, options) with explicit checks
  instead of blind casts, plus unit tests
- Type value-object fromRow() params as stdClass (what wpdb returns) and map
  columns through Val so unexpected shapes degrade safely
- Use %i identifier placeholders for table names in all wpdb::prepare() calls
  so every query string is a literal and identifiers are escaped by WordPress;
  raises the minimum WordPress version to 6.2 where %i was introduced
- Guard wpdb::prepare() null result before wpdb::query() in updateTax()
- Fix nullable get_permalink()/strtotime() handling, list types at REST and
  capability call sites, dead null-coalescing on checked superglobals, and
  narrow get_users() results before mapping
- Register Val method names with the ValidatedSanitizedInput sniff so it
  validates the real sanitizer around each superglobal read
- Update repository unit tests for the %i placeholder arguments

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CLAUDE.md

@@ -70,6 +70,7 @@ All database access goes through repository classes within their domain package.
 | `ShortcodeRegistrar` | Registers `[us_booking]` and `[us_student_login]` shortcodes |
 | `BlockRegistrar` | Registers Gutenberg dynamic-block wrappers for the shortcodes |
 | `BlockPreview` | Static editor-preview markup for the blocks |
+| `Val` | Runtime coercion of untyped WP boundary values (wpdb rows, REST params, superglobals) |
 | `Auth\RoleManager` | Registers `us_instructor` and `us_student` roles with custom caps |
 | `Auth\LoginPage` | Renders front-end student login form |
 | `Availability\AvailabilitySlot` | Immutable value object for a slot row |
@@ -108,6 +109,6 @@ All test classes extend `tests/Unit/TestCase.php`, which handles `Monkey\setUp()
 ### CI
 Gitea Actions (`.gitea/workflows/ci.yml`) runs on every push and pull request:
 - **lint** — PHPCS WordPress coding standards
-- **static-analysis** — PHPStan level 6
+- **static-analysis** — PHPStan level 10
 - **test** — PHPUnit on PHP 8.1, 8.2, 8.3
 - **no-debug** — rejects commits with `var_dump`, `error_log`, etc. in `src/`