feat: replace console logging with proper logger to OpenCode log file (#17)

* Add logger design spec

* feat: add logger module with warn/debug levels

* refactor: replace console calls with logger in plugin.ts

* refactor: replace console calls with logger in models.ts

* refactor: replace console calls with logger in models-dev.ts

* refactor: replace console calls with logger in omniroute-combos.ts

* refactor: address code review feedback and fix pre-existing test failures

- Remove redundant try/catch around findCurrentLogFile() (review)
- Restore specific config values in warning messages (review)
- Fix models.test.mjs to only count /v1/models fetches
- Return empty responses for combo/models.dev endpoints in tests
- All 22 tests now passing

* chore(release): bump version to 1.1.3