Dart 3.9 / Flutter 3.35 [first LLM release] (#2714)

I got carried away with Gemini and basically rewrote CI and the release
process for the new LLM reality. This work was largely completed by
Gemini.

- Bump all SDK versions to the current beta (3.9.0-0)
- Run `flutter channel beta`
- Wrote `ci_script.dart` to replace the bash scripts
- Converted repository to pub workspace #2499 
- Added llm.md and release.md
- Added redirect for deprecated Samples Index

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

compass_app/server/analysis_options.yaml

@@ -1,30 +0,0 @@
-# This file configures the static analysis results for your project (errors,
-# warnings, and lints).
-#
-# This enables the 'recommended' set of lints from `package:lints`.
-# This set helps identify many issues that may lead to problems when running
-# or consuming Dart code, and enforces writing Dart using a single, idiomatic
-# style and format.
-#
-# If you want a smaller set of lints you can change this to specify
-# 'package:lints/core.yaml'. These are just the most critical lints
-# (the recommended set includes the core lints).
-# The core lints are also what is used by pub.dev for scoring packages.
-
-include: package:lints/recommended.yaml
-
-# Uncomment the following section to specify additional rules.
-
-# linter:
-#   rules:
-#     - camel_case_types
-
-# analyzer:
-#   exclude:
-#     - path/to/excluded/files/**
-
-# For more information about the core and recommended set of lints, see
-# https://dart.dev/go/core-lints
-
-# For additional information about configuring this file, see
-# https://dart.dev/guides/language/analysis-options