v0.1.12 SetConsoleWriter routes console output to a host writer

A host that draws on the terminal (a TUI) cannot let the logger write to
stdout or stderr, yet the records are worth showing inside the host.
SetErrorHandler already covers internal diagnostics; SetConsoleWriter is
its sibling for console output.

- SetConsoleWriter(w) sends console output of every console_target to w,
  split's warn-and-above records included; nil restores stdout/stderr.
  It holds across ApplyConfig and is safe while logging.
- One stored value: ApplyConfig and SetConsoleWriter publish the console
  writers through storeConsole; the processor's split branch now reads
  the stored warn writer instead of writing os.Stderr directly.
- TestLoggerConsoleTargets becomes TestConsoleWriterTakesEveryTarget,
  which asserts where each target's records land; a second test checks
  that nil restores the configured writers.
- README names both hooks for terminal hosts; the API doc's callback
  contract covers console writers.

Verified: go build ./... ok; gofmt -l on changed files clean; go vet ./...
ok; go test ./... ok (all four packages, under 1 s); go test -race on the
new tests ok; mutation run 6 of 6 caught.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SyaMAhyEzAp3ULLWJZG4jQ

README.md

@@ -71,6 +71,8 @@ Applications enqueue records into a bounded channel. A single background process
 
 Call `ApplyConfig` (or `Build`) and then `Start` before logging. `Stop` drains accepted records and can be followed by `Start`. `Shutdown` also closes the file; after a timeout, retry it to finish cleanup. See the [API reference](doc/api.md) for ownership and concurrency rules.
 
+Hosts that own the terminal, such as TUIs, route console output with `SetConsoleWriter` and internal diagnostics with `SetErrorHandler`.
+
 ## Contributing
 
 Contributions and suggestions are welcome!