feat(observability): add structured logging

docs/docs/api/appkit/Class.AppKitError.md

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+# Abstract Class: AppKitError
+
+Defined in: [appkit/src/errors/base.ts:33](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L33)
+
+Base error class for all AppKit errors.
+Provides a consistent structure for error handling across the framework.
+
+## Example
+
+```typescript
+// Catching errors by type
+try {
+  await lakebase.query("...");
+} catch (e) {
+  if (e instanceof AuthenticationError) {
+    // Re-authenticate
+  } else if (e instanceof ConnectionError && e.isRetryable) {
+    // Retry with backoff
+  }
+}
+
+// Logging errors
+console.error(error.toJSON()); // Safe for logging, sensitive values redacted
+```
+
+## Extends
+
+- `Error`
+
+## Extended by
+
+- [`AuthenticationError`](Class.AuthenticationError.md)
+- [`ConfigurationError`](Class.ConfigurationError.md)
+- [`ConnectionError`](Class.ConnectionError.md)
+- [`ExecutionError`](Class.ExecutionError.md)
+- [`InitializationError`](Class.InitializationError.md)
+- [`ServerError`](Class.ServerError.md)
+- [`TunnelError`](Class.TunnelError.md)
+- [`ValidationError`](Class.ValidationError.md)
+
+## Constructors
+
+### Constructor
+
+```ts
+new AppKitError(message: string, options?: {
+  cause?: Error;
+  context?: Record<string, unknown>;
+}): AppKitError;
+```
+
+Defined in: [appkit/src/errors/base.ts:49](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L49)
+
+#### Parameters
+
+| Parameter | Type |
+| ------ | ------ |
+| `message` | `string` |
+| `options?` | \{ `cause?`: `Error`; `context?`: `Record`\<`string`, `unknown`\>; \} |
+| `options.cause?` | `Error` |
+| `options.context?` | `Record`\<`string`, `unknown`\> |
+
+#### Returns
+
+`AppKitError`
+
+#### Overrides
+
+```ts
+Error.constructor
+```
+
+## Properties
+
+### cause?
+
+```ts
+readonly optional cause: Error;
+```
+
+Defined in: [appkit/src/errors/base.ts:44](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L44)
+
+Optional cause of the error
+
+***
+
+### code
+
+```ts
+abstract readonly code: string;
+```
+
+Defined in: [appkit/src/errors/base.ts:35](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L35)
+
+Error code for programmatic error handling
+
+***
+
+### context?
+
+```ts
+readonly optional context: Record<string, unknown>;
+```
+
+Defined in: [appkit/src/errors/base.ts:47](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L47)
+
+Additional context for the error
+
+***
+
+### isRetryable
+
+```ts
+abstract readonly isRetryable: boolean;
+```
+
+Defined in: [appkit/src/errors/base.ts:41](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L41)
+
+Whether this error type is generally safe to retry
+
+***
+
+### statusCode
+
+```ts
+abstract readonly statusCode: number;
+```
+
+Defined in: [appkit/src/errors/base.ts:38](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L38)
+
+HTTP status code suggestion (can be overridden)
+
+## Methods
+
+### toJSON()
+
+```ts
+toJSON(): Record<string, unknown>;
+```
+
+Defined in: [appkit/src/errors/base.ts:68](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L68)
+
+Convert error to JSON for logging/serialization.
+Sensitive values in context are automatically redacted.
+
+#### Returns
+
+`Record`\<`string`, `unknown`\>
+
+***
+
+### toString()
+
+```ts
+toString(): string;
+```
+
+Defined in: [appkit/src/errors/base.ts:84](https://github.com/databricks/appkit/blob/main/packages/appkit/src/errors/base.ts#L84)
+
+Create a human-readable string representation
+
+#### Returns
+
+`string`