feat: Add module validation and --list-modules flag to build.py (closes #10)

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Module Validation and --list-modules Flag

This PR adds module validation helpers and a --list-modules flag to build.py.

Changes:

• Added parse_module_selection(): Parses comma-separated module names with optional spaces
• Added validate_module_names(): Validates module names against available modules
• Added list_modules(): Prints available modules with details
• Updated --list flag to use list_modules()
• Updated module selection to use validation helpers
• Added comprehensive unit tests

Acceptance Criteria:

• Validate every name passed to --module before running build commands
• Exit non-zero with invalid name and list of valid module names
• Support comma-separated names with optional spaces
• Add --list-modules flag with module details
• Add unit-testable helper functions

Test Results:

test_single_module ... ok
test_multiple_modules ... ok
test_with_spaces ... ok
test_all_keyword ... ok
test_empty_string ... ok
test_whitespace_only ... ok
test_valid_module ... ok
test_invalid_module ... ok
test_mixed_valid_invalid ... ok
test_all_keyword ... ok

Ran 10 tests in 0.001s
OK

Usage:

# List all modules
python3 build.py --list-modules

# Build with validation
python3 build.py -m backend,frontend

# Invalid module shows error
python3 build.py -m nonexistent
# Output: ✗ Unknown modules: nonexistent
#         Available: backend, frontend, market, ...

Closes #10

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Bounty: $35
Lightning Address: fullphone56@walletofsatoshi.com