docs: fix issues found in planning document review

Riverpod updated to 3.2+ (Dart 3.7+), deployment platform set
to TBD, riverpod_generator updated to ^4.0.2.

docs/implementation-plan.md

@@ -5,7 +5,7 @@ Detailed architecture and build plan for IdeaForge.
 ## decisions
 
 - **Backend:** Python 3.11+, FastAPI, async SQLAlchemy, Pydantic, structlog, Anthropic SDK
-- **Frontend:** Flutter 3.27+, Riverpod 3.1+ (generator syntax), GoRouter, dio, fl_chart
+- **Frontend:** Flutter 3.27+, Riverpod 3.2+ (generator syntax), GoRouter, dio, fl_chart
 - **Database:** SQLite (file-based, persistent Docker volume)
 - **Relationship to idea_manager:** Fresh codebase with core code ported (not fork, not dependency)
 - **Authentication:** None for v1 — demo mode uses middleware protection
@@ -221,9 +221,9 @@ target_audience, category, status (evaluated), tags, and 8 metric scores with re
 dependencies:
   flutter:
     sdk: flutter
-  flutter_riverpod: ^2.6.1
-  riverpod_annotation: ^2.6.1
-  hooks_riverpod: ^2.6.1
+  flutter_riverpod: ^3.2.0
+  riverpod_annotation: ^4.0.1
+  hooks_riverpod: ^3.2.0
   flutter_hooks: ^0.20.5
   go_router: ^14.8.1
   dio: ^5.7.0
@@ -240,7 +240,7 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   build_runner: ^2.4.13
-  riverpod_generator: ^2.6.3
+  riverpod_generator: ^4.0.2
   freezed: ^2.5.7
   json_serializable: ^6.9.0
   very_good_analysis: ^6.0.0
@@ -406,7 +406,7 @@ Retry interceptor: 2 retries on 502/503/504 and connection timeouts only.
             │
    ┌────────▼────────┐
    │  Docker Container │
-   │  (Fly.io/Railway) │
+   │  (platform TBD)   │
    │                    │
    │  FastAPI serves:   │
    │  - /api/* routes   │
@@ -420,7 +420,8 @@ Retry interceptor: 2 retries on 502/503/504 and connection timeouts only.
 ```
 
 Single container. FastAPI serves both the API and the Flutter Web build as static files
-via `StaticFiles` mount. No CORS issues, single deployment target.
+via `StaticFiles` mount. No CORS issues, single deployment target. Hosting platform to
+be decided at deployment time (candidates: Fly.io, Railway, self-hosted).
 
 ### build pipeline