Add beachball config get and config list commands

[ecraig12345]

Summary

Adds beachball config get <name> and beachball config list commands for inspecting the effective beachball configuration.

Currently the intent of these commands is to be read by humans or AI agents, not parsed. The format is similar to YAML, but keys are never quoted, and there's special logic for values such as functions, class instances, and undefined.

Fixes #1185

config get <name>

Gets the value of a specific config setting, including any per-package or per-group overrides. Supports --package to query the effective value for specific packages (accounting for group membership). Note that logged string values will be quoted, which is different from e.g. git config.

$ beachball config get branch
"origin/main"

$ beachball config get disallowedChangeTypes
Main value: null

Group overrides:
  my-group:
    disallowedChangeTypes: ["major"]
    packageNames: ["pkg-a", "pkg-b"]

$ beachball config get disallowedChangeTypes --package pkg-a
pkg-a: ["major"]

config list

Lists all config settings (including defaults), plus any group and per-package overrides, using YAML-like formatting. (Note that keys are not quoted, so it may not be valid YAML.)

$ beachball config list
Main options (including defaults):
  access: "restricted"
  branch: "origin/main"
  bump: true
  ...

Group overrides:
  my-group:
    packageNames: ["pkg-a", "pkg-b"]
    disallowedChangeTypes: ["major"]

Other changes

• src/logging/formatValue.ts — New YAML-like value formatter with width-aware single-line/multi-line output, used by both commands
• src/options/getCliOptions.ts — Added _extraPositionalArgs support for subcommand parsing
• src/help.ts and docs/cli/config.md — Help text and doc site page for both commands
• .claude/skills/beachball-change-file/SKILL.md — Updated to use beachball config get instead of manually reading config files