fix: resolve unit test performance issue and update documentation

## Critical Fixes

### Unit Test Performance (src/main/kotlin/it/saabel/kotlinnotionclient/NotionClient.kt)
- Fixed critical bug where unit tests timed out (2+ minutes → 400ms)
- Root cause: `createWithClient()` used reflection and created real HTTP client before replacing with mock
- Solution: Refactored to use constructor-based dependency injection
- Removed reflection hack, now uses clean `@JvmOverloads` constructor pattern
- Tests now complete in ~400ms as expected for mocked tests

### Client Instantiation Pattern
- Made primary constructor public with optional HttpClient parameter
- Supports both patterns:
  - `NotionClient(apiToken)` - Direct constructor (idiomatic Kotlin)
  - `NotionClient.create(apiToken)` - Factory method (also supported)
- No deprecation - both are first-class citizens

## Documentation Updates

### Updated All Documentation to Constructor Pattern
- README.md: Added client initialization section, shows both patterns
- QUICKSTART.md: Updated examples, fixed old package name (no.saabelit → it.saabel)
- docs/*.md: Updated 6 API doc files (blocks, error-handling, notebooks, search, testing, users)
- All examples now use `NotionClient(token)` as primary pattern
- Clearly documents that both patterns are fully supported

### Integration Tests
- Updated 13 integration test files to use constructor pattern
- Files: All pagination tests, DataSourcesIntegrationTest, DatabaseQueryIntegrationTest,
  EnhancedFileUploadIntegrationTest, NotionClientIntegrationTest, RateLimitVerificationTest
- Pattern: `NotionClient.create(NotionConfig(...))` → `NotionClient(NotionConfig(...))`

## Developer Experience Improvements
- Added journal entry documenting DX exploration session findings
- Removed obsolete phase completion files (PHASE1_COMPLETE.md, PRE_PUBLICATION_SECURITY_REVIEW.md, README-DRAFT.md)
- Added docs/notebooks.md for Jupyter notebook integration examples

## Verification
- ✅ All unit tests pass (~400ms execution time)
- ✅ Build succeeds
- ✅ Documentation consistent across all files
- ✅ Both instantiation patterns work correctly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: Jonas Saabel

PHASE1_COMPLETE.md

@@ -17,18 +17,18 @@ Get started with the Kotlin Notion Client in under 5 minutes.
 
 ```kotlin
 dependencies {
-    implementation("no.saabelit:kotlin-notion-client:0.1.0")
+    implementation("it.saabel:kotlin-notion-client:0.1.0")
 }
 ```
 
 ## Your First API Call
 
 ```kotlin
-import no.saabelit.kotlinnotionclient.NotionClient
+import it.saabel.kotlinnotionclient.NotionClient
 
 fun main() = runBlocking {
     // Initialize the client
-    val notion = NotionClient.create("your-api-token")
+    val notion = NotionClient("your-api-token")
 
     // Get current user (verifies token works)
     val user = notion.users.getCurrentUser()
@@ -39,6 +39,26 @@ fun main() = runBlocking {
 }
 ```
 
+### Client Initialization
+
+You can create a `NotionClient` instance using either pattern:
+
+```kotlin
+// 1. Direct constructor (recommended - idiomatic Kotlin)
+val notion = NotionClient("your-api-token")
+
+// 2. Factory method (also supported)
+val notion = NotionClient.create("your-api-token")
+
+// With custom configuration
+val notion = NotionClient(
+    NotionConfig(
+        apiToken = "your-api-token",
+        logLevel = LogLevel.INFO
+    )
+)
+```
+
 ## Understanding the 2025-09-03 API
 
 **Important**: Before going further, understand this key concept:
@@ -226,7 +246,7 @@ notion.close()
 Or use `.use` for automatic cleanup:
 
 ```kotlin
-NotionClient.create("token").use { notion ->
+NotionClient("token").use { notion ->
     // Your code here
 }
 ```