feat(issue-#36): add Dockerfile + docker-compose for local dev

[QW1CKS]

Multi-stage build using oven/bun with Playwright Chromium support. docker-compose configured for interactive CLI mode with .env and persistent settings volume.

[Copilot]

Pull request overview

Adds containerization for running Dexter locally via Docker, targeting a Bun-based runtime with Playwright Chromium available and an interactive TTY for the Ink CLI.

Changes:

• Add Dockerfile with multi-stage Bun build and explicit Playwright Chromium installation.
• Add docker-compose.yml service configured for interactive CLI usage and persistent .dexter settings.
• Add .dockerignore to reduce build context and prevent copying local secrets/state.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
docker-compose.yml	Defines a dexter service for interactive CLI runs and persists /app/.dexter via a named volume.
Dockerfile	Builds a Bun image, installs OS deps for Chromium, copies dependencies, and installs Playwright Chromium.
.dockerignore	Excludes common local/dev artifacts and secrets from the Docker build context.

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[Copilot]

bun install --frozen-lockfile will still execute the postinstall script from package.json (which runs playwright install chromium). As written, the deps stage will download Chromium once during bun install, and the final stage downloads it again in the explicit bunx playwright install chromium step. Consider setting PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD=1 (or otherwise disabling postinstall) for the deps stage, so the browser is downloaded exactly once in the final stage (or alternatively copy the Playwright browser cache from the deps stage into the final stage).

[Copilot]

The comment about Playwright install being skipped because postinstall "only runs in non-frozen mode" appears inaccurate given the repo’s postinstall script and is likely to confuse future maintainers. Please update the comment to reflect the real reason for the explicit install (e.g., browser binaries aren’t copied from the deps stage / are stored in the Playwright cache path).

Suggested change

	# Install Playwright Chromium (skipped in bun install since postinstall
	# only runs in non-frozen mode; install it explicitly here)
	# Install Playwright Chromium explicitly because the browser binaries are not
	# included when copying node_modules from the deps stage (they live in the