Merge SUGGESTIONS.md into TODO.md; silence 300+ unconditional DEBUG prints

[Copilot]

Merges SUGGESTIONS.md into TODO.md (then deletes it), and implements Sprint 1.1/1.2: gating all codegen/semantic DEBUG output behind a runtime flag and removing the global VERBOSE compile definition that was enabling parser traces for every build.

SUGGESTIONS.md → TODO.md

• Added §10 Consistency & Polish with all sprint items (DEBUG silencing, doc consolidation, Vec/String/borrow consistency)
• Added Architecture Notes section (immutable AST separation, IR opt phase, parser error recovery)
• Extended 1.0 Release Criteria with: silent-by-default, ownership tests, FFI tests, complete string methods
• Fixed duplicate §10 numbering (Async bumped to §11)

Silence DEBUG output

semantic.hpp now declares a shared runtime flag and convenience macro:

namespace vyn { extern bool g_debug_codegen; }  // false by default
#define VDBG(stmt) do { if (vyn::g_debug_codegen) { stmt; } } while(0)

• --verbose CLI flag added to main.cpp to enable at runtime
• All 300+ std::cout/cerr << "DEBUG:" prints across 15 files in src/vre/ wrapped with VDBG() or if (vyn::g_debug_codegen) (multi-statement blocks handled explicitly)
• Removed add_compile_definitions(VERBOSE) from CMakeLists.txt — this was the root cause of [PEEK]/[CONSUME]/[EXPECT] parser traces appearing in every normal run
• Wrapped the remaining unguarded [ModuleParser] traces in module_parser.cpp with #ifdef VERBOSE; fixed \\\\n escape literals while there

Normal run is now silent. --verbose restores full debug output for development.

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