refactor: switch the whole project to English

talk is going to be published. Code comments, CLI output, error messages,
daemon log lines, MCP descriptions and results, test names and assertions,
README, spec, skill, build scripts and flake are now English. Only the
spoken announcement texts stay bilingual: the wrap result and the test
sentence are German or English depending on the detected language.

Language fallback is now configurable: `lang = "en" | "de"` (env
TALK_LANG, default en) is used when detection cannot tell (numbers, single
words, ties) and for talk's own announcements. langdetect.Detect takes the
fallback as an argument instead of hard-coding German. `talk setup` asks for
it; `talk doctor` and `talk status` show it.

Vocabulary pinned across packages so the process-boundary tests observe
stable strings: chain log lines ("chain: tier X skipped (not available)",
"falling back to the next tier", "spoken via X"), queue lines ("discarded:
quiet hours ... active", "replaced by toast", "max_age"), CLI notes
("speaking directly", "daemon started at", "no daemon", "nothing to cancel"),
status block with aligned English labels, MCP messages, origin guard 403.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/audio/doc.go

@@ -1,5 +1,5 @@
-// Package audio implementiert die Audio-Ausgabe von talk über das
-// Sink-Interface: Playback embedded via oto (RIFF/WAVE-PCM und MP3, per
-// reinem Go-Dekodierer) und ein null-Sink, das verwirft (CI, Server,
-// Tests). Auswahl per Config audio.sink = "oto" | "null" (Default oto).
+// Package audio implements talk's audio output behind the Sink interface:
+// embedded playback via oto (RIFF/WAVE PCM and MP3, via a pure Go decoder)
+// and a null sink that discards (CI, servers, tests). Selected via config
+// audio.sink = "oto" | "null" (default oto).
 package audio