Approved gong voicing: 220Hz fundamental, fatter mids, -7dBFS at vol 75

User verdict: audible and butler-non-intrusive on the bare 2W speaker.
Recorded as the house sound signature in architecture.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/architecture.md

@@ -144,6 +144,12 @@ ported to LVGL. The `STATES` table in the sim defines the contract:
 | `rage` | — | — | 34 fast streams | 3-frame kaomoji loop through the eyes slot: `(°□°) ┬─┬` → `(╯°□°)╯︵ ┻━┻` → `┬─┬ ノ( º_º ノ)` — flips the table, then composes itself and puts it back |
 | `error` | `x   x` | `-` | none (rain dies) | face dims to 45% |
 
+**Sound signature**: the cathedral gong (`play_boot_gong` in firmware — 220 Hz
+inharmonic partial stack, feedback-comb reflections, ~-7 dBFS) is the approved house
+sound: "audible and butler-non-intrusive." Plays at boot; planned as the
+wake-from-`dormant` sound. Tune by adjective: tail = `tau`s, cathedral size = echo
+delays, depth = fundamental, presence = `GONG_PEAK`/`GONG_VOLUME`.
+
 **Wait cues are a hard requirement** (user-stated): Tatlock turns take 10–25 s, so
 `effort` must always show *alive-and-working* signals — the orbiting bezel arc, the
 elapsed-seconds counter, and max rain. Never a bare static face during a wait, and no