refactor: send all logging to stderr through an injectable Logger

[IvanKiral]

Motivation

logInfo wrote to console.log — stdout. Harmless while every command prints prose, but the mapi command this branch builds on writes a response body to stdout. At that point every progress line lands inside the payload: kontent mapi content-types > types.json puts log lines in the JSON, | jq dies on the first one. Fixing the boundary before mapi emits a payload means it lands correct instead of being retrofitted.

What changed

• All logging goes to stderr, unconditionally. stdout is reserved for command payloads. This is the POSIX meaning of stderr — diagnostics, not just errors — and how curl, git and npm behave.
• logInfo/logWarning/logError/isVerbose are replaced by a Logger closure. Handlers build it once with createLoggerFromArgs(args) and pass it down; core takes a Logger parameter or carries it in deps, so it no longer sees LogOptions and can be tested by injecting a sink instead of stubbing console.
• Colour on stderr comes from chalkStderr. chalk derives its level from stdout, so a piped stdout would otherwise strip colour from a stderr that is still a terminal.
• New src/lib/ui/prompts.ts binds @clack/prompts to stderr in one place rather than at every call site. Side effect: spinners keep animating when stdout is piped, because clack's TTY check reads the stream it is handed.
• --logLevel is typed end to end. LogLevel derives from the choices tuple, so yargs infers the union; LogOptions stays the flat parser shape and is collapsed into a single level by createLoggerFromArgs.

No user-facing change — --logLevel, --ll, --verbose and KONTENT_LOG_LEVEL behave exactly as before.

Checklist

• Code follows coding conventions held in this repo
• Automated tests have been added — existing tests updated to the new signatures; no new behaviour to cover
• Tests are passing
• Docs have been updated (CLAUDE.md: output-channel rule and the Logger convention)
• Temporary settings have been reverted to defaults

How to test

kontent telemetry status 2>/dev/null              # stdout is empty
kontent telemetry status --verbose 1>/dev/null    # every diagnostic still visible
kontent telemetry status --ll bogus               # rejected by yargs choices
kontent project sample bootstrap --envId <id>     # spinners, prompts, notes render
kontent project sample bootstrap --envId <id> 1>/dev/null   # still usable, now on stderr