docs: fix .spi.yml and DocC warning to unblock SPI documentation build

- Remove unsupported platform/swift_version fields from .spi.yml
  (match apple/swift-nio's minimal format — just documentation_targets)
- Fix broken DocC symbol link: columnNotFound -> columnNotFound(_:)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: vkuttyp

.spi.yml

@@ -7,5 +7,3 @@ builder:
         - CosmoPostgres
         - CosmoMySQL
         - CosmoSQLite
-      swift_version: "6.0"
-      platform: macosSpm

Sources/CosmoSQLCore/SQLRow.swift

@@ -37,7 +37,7 @@ public struct SQLRow: Sendable {
 // MARK: - Helpers
 
 public extension SQLValue {
-    /// Throws ``SQLError/columnNotFound`` when the value is `.null` and was
+    /// Throws ``SQLError/columnNotFound(_:)`` when the value is `.null` and was
     /// produced by a missing column lookup.
     func require(column: String = "<unknown>") throws -> SQLValue {
         if case .null = self {