Upgrade Fix

Apply all upgrade changes end-to-end: version pins, gem dependencies, code fixes, Rails config (if Rails), iterative RSpec green, iterative RuboCop green.

Argument Parsing

Two modes:

Explicit mode:

• ruby:X.Y.Z — required target Ruby version
• rails:X.Y — optional target Rails version
• scope:path — optional; restricts code-level fixes to this file or directory. Gem and version pin changes always apply project-wide.

Next mode:

• next (bare keyword, no value) — resolve the target from the task list created by /plan. See Step 1b below.

next is mutually exclusive with ruby:/rails:. If both are given, surface an error and stop. If neither is given, surface: Provide either 'next' (requires a plan) or 'ruby:X.Y.Z [rails:X.Y]'.

Step 0: Load custom rules (if present)