feat(pins): Trinity Pins DSL - Single Source of Truth

[gHashTag]

Add pins DSL parser with lexer, parser, AST, and XDC emitter

• Lexer with proper token types (keywords, identifiers, strings, punctuation)
• Recursive descent parser for board, fabric, and design files
• XDC emitter that generates Vivado-compatible constraint files
• CLI commands: tri fpga pins {to-xdc|validate|ir|doctor}

Files:

• src/tri/pins_parser.zig - Full DSL implementation (~1400 LOC)
• src/tri/tri_fpga.zig - CLI routing for fpga pins commands
• fpga/boards/qmtech_xc7a100t.board.tri - Board definition with connectors
• fpga/designs/uart_bridge_fixed.design.tri - Test design binding

Features:

• Single source of truth for pin mapping
• Declarative DSL syntax
• Support for board, fabric, and design files
• Generates XDC, IR, and validation reports

Status: ✅ Ready for review