refactor: Unify leggen and leggend packages into single leggen package

- Merge leggend API components into leggen (api/, services/, background/)
- Replace leggend command with 'leggen server' subcommand
- Consolidate configuration systems into leggen.utils.config
- Update environment variables: LEGGEND_API_URL -> LEGGEN_API_URL
- Rename LeggendAPIClient -> LeggenAPIClient
- Update all documentation, Docker configs, and compose files
- Fix all import statements and test references
- Remove duplicate utility files and clean up package structure

All tests passing (101/101), linting clean, server functionality preserved.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.pre-commit-config.yaml

@@ -15,8 +15,8 @@ repos:
     hooks:
       - id: mypy
         name: Static type check with mypy
-        entry: uv run mypy leggen leggend --check-untyped-defs
-        files: "^leggen(d)?/.*"
+        entry: uv run mypy leggen --check-untyped-defs
+        files: "^leggen/.*"
         language: "system"
         types: ["python"]
         always_run: true