Add devcontainer support for Codespaces, local, and Claude Code

[abkfenris]

Adds .devcontainer/devcontainer.json (docker-compose based, reusing the
existing dev target/services) with:

• git, github-cli, and common-utils features for a usable shell/terminal
• the official Claude Code devcontainer feature, with CLAUDE_CONFIG_DIR
  pointed at a persisted volume so login survives rebuilds
• docker-outside-of-docker so docker compose logs works from the
  integrated terminal (requires moby:false, since moby packages aren't
  published for Debian trixie)
• forwarded ports for the app, Sentry Spotlight, and Storybook

Removes the old root-level devcontainer.json, which pointed at a
nonexistent workspace path and predates the .devcontainer/ convention.

Requires the Dockerfile syntax bump to 1.4: devcontainer feature injection
uses BuildKit named build contexts, which aren't supported under 1.2.

Also bakes Playwright's browsers into the dev image (otherwise lost every
time the devcontainer is recreated) so npm run test:e2e and the Storybook
vitest addon work out of the box, pins the compose port mappings to
0.0.0.0 (Docker's default dual-stack publish was confusing VS Code's port
forwarding into offering a non-working [::1] address), and allow-lists
localhost/127.0.0.1 as Next.js dev origins for the same forwarded-port
reason.

Fixes an unrelated Storybook glob that never matched any files (all
stories are .tsx; the plain .[jt]s pattern only matches .js/.ts) and was
printing a spurious "no story files found" warning on every start.