v0.5.1: Fix C/C++/CUDA/GLSL function extraction, add config linker and tests

- Fix extract_defs.c declarator chain traversal for C-family function_definition
  nodes (off-by-one in field name length, missing depth traversal)
- Add resolve_func_name() support for CommonLisp defun, Makefile rule, VimScript,
  Julia, Elm value_declaration, Groovy field_function methods
- Add config linker pipeline: 3 strategies linking config keys to code symbols,
  dependency manifest entries to imports, and config file path references
- Add regression tests (~150 cases across 50+ languages), language failure tests,
  and config extraction tests
- Refactor discover.go, configures.go, configlink_strategies.go to reduce
  cognitive complexity (extract helpers for gocognit compliance)
- Fix Louvain community detection: use map lookup instead of O(N) scan