dx: add --verbose/--debug CLI flags and config validation command

[rohilsurana]

Problem

Several developer experience gaps in the CLI:

1. No `--verbose`/`--debug` flags — when builds fail or config is wrong, there's no way to get detailed output. Config parse errors are silently swallowed by `loadConfig()`.
2. No `chronicle validate` command — no way to check config validity without starting the server. Useful in CI pipelines.
3. CLI version hardcoded to `'0.1.0'` in `src/cli/index.ts` — should be read from `package.json`.
4. Dev server doesn't check port conflicts — starts without warning if the port is already in use.
5. Build doesn't report bundle size — no output size summary or warnings for large bundles.

Suggested Fix

• Add `--verbose` global flag that enables debug logging throughout the config loader, build, and dev server
• Add a `chronicle validate` command that parses config, checks content dirs exist, validates API spec files are readable, and reports issues
• Read version from `package.json` at build time
• Check port availability before starting dev server, suggest next available port