feat(migrations): introduce model-aware operations, flat discovery, and colored CLI output

[Einswilli]

PR Description

Overview

This PR significantly upgrades the Ryx migration engine and CLI. The key goal is to make migrations fully multi-database aware, self-documenting in their generated code, and provide a much better developer experience with colored terminal output in the CLI.

We've also refactored the migration runner to use a flat-discovery strategy, allowing migration files to be shared and selectively applied based on the database alias.

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Key Changes

1. Colored & Styled CLI

• New style.py utility module: Detects terminal color support and provides helpers (PREFIX, OK, FAIL, WARN, red, green, cyan...).
• Updated CLI commands: makemigrations and migrate now output colored, nicely formatted messages.
• Cleanup: Removed dead --plan handling and unused imports in the migrate command.

2. Model-Aware Migration Operations

• Inject Model references: CreateTable, AddField, AlterField, and CreateIndex operations now optionally carry a reference to the Python Model class they originated from.
• Auto-generated imports: The Autodetector collects these models and automatically writes from app.models import ModelA, ModelB at the top of generated migration files, making them fully runnable without manual edits.
• Pretty-printed operations: to_python() methods now output multi-line, readable code rather than single-line dense strings.

3. Flat Discovery & Per-Alias Routing

• Global file discovery: The migration runner now recursively finds all [0-9]*.py files under the migrations/ directory (ignoring __pycache__).
• Per-alias filtering: Each file's operations are filtered at runtime via _operation_is_relevant() to only execute ops relevant to the current database alias (based on model._meta.database or the Router).
• Qualified tracking keys: The ryx_migrations table now stores alias|stem keys (with backward compatibility for bare stems), allowing the same migration file to be marked as applied independently for different databases.

4. Interactive Fallback

• The migrate command's interactive fallback (when no migration files are found) now uses the colored style module for a friendlier UX. It also gained --no-interactive support for CI environments to prevent hanging on input().

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How to Test

1. Run the CLI commands with a real model setup:

   ryx makemigrations --models myapp.models
   ryx migrate

2. Verify the generated migration file is a runnable Python file (auto-imports work, no NameError).
3. Test multi-DB by routing different models to different aliases and running ryx migrate twice (the second run should be a no-op).