docs: add comprehensive Riverpod 3.0 migration documentation and Priority 1 implementation

Priority 1 (COMPLETE):
- Add riverpod_lint and custom_lint packages
- Update analysis_options.yaml with custom_lint plugin
- Update AGENTS.md with Riverpod 3.0 best practices
- Fix unsafe ref usage in modern_chat_input.dart
- All tests passing, zero breaking changes

Priority 2 (PLANNED):
- Complete migration plan for 39 providers (RIVERPOD_PRIORITY2_PLAN.md)
- Quick reference guide (RIVERPOD_PRIORITY2_QUICKREF.md)
- Progress tracker (RIVERPOD_PRIORITY2_TRACKER.md)
- Master documentation index (RIVERPOD_MIGRATION_INDEX.md)
- Analysis and summary documents

Documentation includes:
- Step-by-step migration examples
- 6-phase implementation plan (23-33 hours)
- Testing strategies and rollback procedures
- Risk assessment and mitigation
- Timeline and resource estimates

pubspec.lock

@@ -177,6 +177,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.0.4"
+  ci:
+    dependency: transitive
+    description:
+      name: ci
+      sha256: "145d095ce05cddac4d797a158bc4cf3b6016d1fe63d8c3d2fbd7212590adca13"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.0"
   cli_config:
     dependency: transitive
     description:
@@ -185,6 +193,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.2.0"
+  cli_util:
+    dependency: transitive
+    description:
+      name: cli_util
+      sha256: ff6785f7e9e3c38ac98b2fb035701789de90154024a75b6cb926445e83197d1c
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.4.2"
   clock:
     dependency: transitive
     description:
@@ -257,6 +273,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.0.8"
+  custom_lint:
+    dependency: "direct dev"
+    description:
+      name: custom_lint
+      sha256: "78085fbe842de7c5bef92de811ca81536968dbcbbcdac5c316711add2d15e796"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.8.0"
+  custom_lint_builder:
+    dependency: transitive
+    description:
+      name: custom_lint_builder
+      sha256: cc5532d5733d4eccfccaaec6070a1926e9f21e613d93ad0927fad020b95c9e52
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.8.0"
   custom_lint_core:
     dependency: transitive
     description:
@@ -573,6 +605,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.7.0"
+  hotreloader:
+    dependency: transitive
+    description:
+      name: hotreloader
+      sha256: bc167a1163807b03bada490bfe2df25b0d744df359227880220a5cbd04e5734b
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.3.0"
   html:
     dependency: transitive
     description:
@@ -1061,6 +1101,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "3.0.0"
+  riverpod_lint:
+    dependency: "direct dev"
+    description:
+      name: riverpod_lint
+      sha256: "89bce8d40bed52aa89b43ef45cfe473a9c7736629d61fc659c95e4e9f4d571a6"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.0"
   rxdart:
     dependency: transitive
     description: