chore: Replace devcontainer with Flox environment and streamline CI

Migrate from Docker-based devcontainer to Flox for reproducible development
environments. This simplifies the setup by using Nix packages (nodejs_24,
claude-code, prettier, markdownlint-cli) and removes redundant configuration
files that have been consolidated elsewhere.

- Remove .devcontainer/ in favor of .flox/ environment
- Remove copilot-instructions.md (consolidated into CLAUDE.md)
- Remove separate claude-code-review.yml workflow
- Update claude.yml with newer tool versions and explicit Node.js setup

Signed-off-by: Eden Reich <eden.reich@gmail.com>

Author: edenreich

.devcontainer/Dockerfile

@@ -0,0 +1 @@
+env/manifest.lock linguist-generated=true linguist-language=JSON

.devcontainer/devcontainer.json

@@ -0,0 +1,5 @@
+run/
+cache/
+lib/
+log/
+!env/

.flox/.gitattributes

@@ -0,0 +1,4 @@
+{
+  "name": "typescript-sdk",
+  "version": 1
+}