fix: USB-faithful out-of-box defaults (1000Hz polling, mic off)

Audit of every default behavior vs a wired-USB DualSense found the firmware already near-identical for input; only two defaults diverged meaningfully:

- polling_rate_mode 0 (250Hz) -> 2 (realtime/1000Hz): match a wired DS5's 1ms input latency instead of polling 4x slower. Mode 2 also bypasses the report-throttle used by the 250/500Hz modes. NEEDS HIL SOAK-TEST (realtime drops the throttle) before this branch merges to master.

- bt_mic_enable 1 -> 0 (off): the BT mic has a known 2x-playback-rate bug (#10), so it is opt-in until root-caused on hardware.

Both only affect fresh flashes / Reset-to-defaults; existing saved configs keep their values.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -8,6 +8,15 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). Version
 
 ## [Unreleased]
 
+### Changed
+
+- **`polling_rate_mode` now defaults to realtime / 1000 Hz** (was 250 Hz) so a fresh flash matches a wired DualSense's 1 ms input latency instead of polling 4× slower. Mode 2 also bypasses the report-throttling used by the 250/500 Hz modes, forwarding every BT input report immediately. Existing saved configs keep their value; this only affects fresh flashes / Reset-to-defaults. (Out-of-box "acts like USB" pass.)
+- **`bt_mic_enable` now defaults to Off** (was On) — the DualSense BT microphone path has a confirmed playback-rate bug (issue #10: recordings come out ~2× too fast / half-duration). Until that's root-caused on hardware, the mic is opt-in: fresh flashes / Reset-to-defaults boot with it off, and it can be turned on from the OLED **Settings** screen (`BT Mic`) or the web config. Existing saved configs keep their current value. (Web config default should be flipped to match in `DS5Dongle-OLED-Config-Web`.)
+
+### Known issues
+
+- **BT microphone records ~2× too fast (#10).** The mic playout stage is wall-clock paced at 10 ms / 480 samples into a 48 kHz endpoint, which should be real-time, so the 2× points at the on-wire frame size/rate differing from the assumed 480 samples. Needs the OLED **Diagnostics** `Mic dec=` (samples per `opus_decode`) and `Mic in/s` (arrival rate) read on hardware to make the fix deterministic — `Mic dec=240` would confirm a half-rate stream. Mic is opt-in (off by default) in the meantime.
+
 ---
 
 ## [0.6.11-oled-edition] — 2026-06-02

src/config.cpp

@@ -67,9 +67,11 @@ void config_valid() {
         body->disable_pico_led = 0;
         printf("[Config] disable_pico_led is invalid\n");
     }
-    if (body->polling_rate_mode > 2) {
+    if (body->polling_rate_mode > 2) {        // 0xFF erased / out of range → default
-        body->polling_rate_mode = 0;
+        body->polling_rate_mode = 2;          // realtime / 1000 Hz — match a wired DS5's
-        printf("[Config] polling_rate_mode is invalid\n");
+                                              // 1 ms polling (was 0 / 250 Hz). Existing
+                                              // saved configs keep their value.
+        printf("[Config] polling_rate_mode invalid, defaulting to 2 (1000 Hz)\n");
     }
     if (body->audio_buffer_length < 16 || body->audio_buffer_length > 128) {
         body->audio_buffer_length = 16;  // low buffer avoids the DS5's periodic re-buffer gap
@@ -109,9 +111,13 @@ void config_valid() {
         body->screen_off_timeout = 15;    // mirrors the original 15-min off tier
         printf("[Config] screen_off_timeout invalid, defaulting to 15 min\n");
     }
-    if (body->bt_mic_enable > 1) {        // 0xFF erased / upgrade → default ON
+    if (body->bt_mic_enable > 1) {        // 0xFF erased / upgrade → default OFF
-        body->bt_mic_enable = 1;
+        body->bt_mic_enable = 0;          // opt-in: the BT mic path has a known
-        printf("[Config] bt_mic_enable invalid, defaulting to 1 (on)\n");
+                                          // 2x-playback-rate bug (#10), so it is
+                                          // off until explicitly enabled (Settings
+                                          // screen / web config). Existing saved
+                                          // configs keep their value.
+        printf("[Config] bt_mic_enable invalid, defaulting to 0 (off)\n");
     }
     if (body->screen_brightness > 3) {    // kBrightLevels has 4 entries (0..3)
         body->screen_brightness = 0;      // full brightness