docs: Add table declaration specification

Comprehensive spec covering:
- Table tiers and class structure
- Definition string grammar
- Attribute types (core, string, temporal, codec)
- Default values and nullable attributes
- Foreign key references and options
- Index declarations
- Part tables
- Auto-populated tables
- Validation rules
- SQL generation

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Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dimitri-yatsenko