refactor(config): delete legacy static ProjectConfigLoader API + orphaned ProjectConfig POJO

With Analyzer and CliOutput migrated off the legacy static API (prior two
commits) and the legacy-only tests rewritten against loadFrom(Path) (prior
two commits), the deprecated surface has no remaining callers.

Removed from ProjectConfigLoader:
- public static boolean loadIfPresent(Path, CodeIqConfig)
- public static ProjectConfig loadProjectConfig(Path)
- package-private static ProjectConfig parseProjectConfig(Map)
- private static applyOverrides / toInt helpers (only used by loadIfPresent)
- LEGACY_CONFIG_FILE_NAMES array (only used by the deleted statics; the
  new surface only honors codeiq.yml and .osscodeiq.yml).

Inlined parseProjectConfig's logic directly into translateLegacyToUnified
so the legacy ProjectConfig POJO has no remaining reference. The
translator now reads languages/detectors/exclude/parsers/pipeline.* in
place from the raw YAML map, without the intermediate POJO.

Deleted:
- src/main/java/io/github/randomcodespace/iq/config/ProjectConfig.java
  (orphaned after inlining)

Kept:
- ProjectConfigLoader#loadFrom(Path) — canonical Phase-B surface.
- ProjectConfigLoader.LoadResult — returned record.
- translateLegacyToUnified + readAndTranslateLegacy + countLegacyKeys —
  internal helpers for the .osscodeiq.yml deprecation shim.

ProjectConfigLoaderTest trimmed: removed 5 tests that exclusively
exercised the deleted legacy-file-name (.code-iq.yml/.yaml) paths plus
the removed return-false-and-mutate-CodeIqConfig semantics. Ported 2
meaningful tests (empty-file handling, invalid-YAML resilience) onto
loadFrom(Path); those pin safety behaviour of the deprecation shim.

Full suite: 3277 -> 3272 tests (-5), 0 failures, 31 skipped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: aksOps