Refactor repository and service composition

[cmyui]

Summary

• add CODE_STYLE.md documenting the repository/service/composition direction we have been using
• convert repository modules from module-level database reach-through to injected repository classes
• move app/usecases to app/services and keep business logic in constructor-injected service classes
• add FastAPI dependency providers for API routes, with each controller declaring the exact service it needs inline
• move v1, v2, bancho login, score leaderboard, and score submission route logic behind services while keeping protocol response formatting in controllers
• split osu-web logic into focused domain services for accounts, beatmap leaderboards, client integrity, comments, direct search, favourites, mail reads, maps/beatmaps, replays, and screenshots
• delete the old app/services/osu_web.py catch-all service bucket
• move public v1 API read SQL into repository Core queries and cover those public read query semantics with repository integration tests
• replace the one-off score submission adapter with explicit composition and a consolidated BanchoAuthenticationService used by login, score submission, and inline osu-web route auth
• keep legacy packet handlers, commands, and active-record object methods on an explicitly named legacy repository bridge until they can be moved behind dedicated service seams
• ignore the local-only osuctl stable-client harness directory

Testing

• uv run mypy app
• uv run --frozen --env-file .env.test pytest tests/unit (217 passed)
• make test (240 passed)
• uv run pre-commit run --all-files
• GitHub checks passing: build, mypy, run-test-suite, pre-commit.ci, task-list-completed

Manual smoke

• stable osu! client smoke was used during this PR to verify login, leaderboard fetch, and failed taiko score submission against the local bancho/nginx stack