refactor: deduplicate and clean up across all source modules

- Extract canonical date algorithm to src/date.rs; remove duplicates in log.rs and detect.rs
- Extract build_std_command in launch.rs; unify needs_host_library_injection via pub(crate) delegation
- Add missing unknown-setting warning to parse_imported_config in share.rs
- Extract format_with_hint helper in error.rs; set_proton_no_sync helper in env.rs
- Remove dead match in completion.rs shell_path_literal; use parse_fps for FpsCap in keys.rs
- Replace six as_str() impls with impl_as_str! macro in schema.rs
- Collapse ResolvedSettings::apply (~110 lines) with apply_scalar!/apply_opt!/apply_clone! macros
- Replace six color functions with color_fn! macro in color.rs

89/89 tests passing, zero clippy warnings.

Co-Authored-By: claude-flow <ruv@ruv.net>

PROJECT_MAP.md

@@ -252,3 +252,4 @@ Do not update this file for:
 - [2026-06-06] Renamed the MangoHud/GameMode settings to `mangohud`/`gamemode` with legacy aliases, and grouped settings help with per-tool filters.
 - [2026-06-06] Removed profile inheritance, flattened resolution to defaults plus one profile, and made config/profile exports sparse.
 - [2026-06-14] Added hook-errors setting (warn/fail) to control pre-launch hook failure behavior; ensured post-hook runs after game spawn failures; propagated game exit codes; centralized hook execution via run_hook().
+- [2026-06-14] Consolidated repeated config string mappings, resolved-setting application, and color helpers with local macros.