feat: full quality tiers + slider UI + key-change warning on Android

1. Wire protocol: add Opus 32k/48k/64k (CodecId 6/7/8) + STUDIO
   profiles with is_opus() helper. Opus enc/dec accept all Opus variants.

2. JNI bridge: expand profile_from_int to 7 levels (0-6) mapping to
   GOOD, DEGRADED, CATASTROPHIC, Codec2_3200, STUDIO_32K/48K/64K.

3. Settings UI: replace radio buttons with Material3 Slider — 7 stops
   from Studio 64k (green) to Codec2 1.2k (dark red), matching desktop.

4. Key-change warning: AlertDialog on connect when server fingerprint
   has changed. Shows old vs new fingerprint, Accept New Key or Cancel.
   Accepting saves the new fingerprint and proceeds with the call.

5. Engine recv: handle studio codec IDs in auto-switch path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/wzp-proto/src/codec_id.rs

@@ -18,6 +18,12 @@ pub enum CodecId {
     Codec2_1200 = 4,
     /// Comfort noise descriptor (silence suppression)
     ComfortNoise = 5,
+    /// Opus at 32kbps (studio low)
+    Opus32k = 6,
+    /// Opus at 48kbps (studio)
+    Opus48k = 7,
+    /// Opus at 64kbps (studio high)
+    Opus64k = 8,
 }
 
 impl CodecId {
@@ -27,6 +33,9 @@ impl CodecId {
             Self::Opus24k => 24_000,
             Self::Opus16k => 16_000,
             Self::Opus6k => 6_000,
+            Self::Opus32k => 32_000,
+            Self::Opus48k => 48_000,
+            Self::Opus64k => 64_000,
             Self::Codec2_3200 => 3_200,
             Self::Codec2_1200 => 1_200,
             Self::ComfortNoise => 0,
@@ -36,8 +45,7 @@ impl CodecId {
     /// Preferred frame duration in milliseconds.
     pub const fn frame_duration_ms(self) -> u8 {
         match self {
-            Self::Opus24k => 20,
-            Self::Opus16k => 20,
+            Self::Opus24k | Self::Opus16k | Self::Opus32k | Self::Opus48k | Self::Opus64k => 20,
             Self::Opus6k => 40,
             Self::Codec2_3200 => 20,
             Self::Codec2_1200 => 40,
@@ -48,7 +56,8 @@ impl CodecId {
     /// Sample rate expected by this codec.
     pub const fn sample_rate_hz(self) -> u32 {
         match self {
-            Self::Opus24k | Self::Opus16k | Self::Opus6k => 48_000,
+            Self::Opus24k | Self::Opus16k | Self::Opus6k
+            | Self::Opus32k | Self::Opus48k | Self::Opus64k => 48_000,
             Self::Codec2_3200 | Self::Codec2_1200 => 8_000,
             Self::ComfortNoise => 48_000,
         }
@@ -63,6 +72,9 @@ impl CodecId {
             3 => Some(Self::Codec2_3200),
             4 => Some(Self::Codec2_1200),
             5 => Some(Self::ComfortNoise),
+            6 => Some(Self::Opus32k),
+            7 => Some(Self::Opus48k),
+            8 => Some(Self::Opus64k),
             _ => None,
         }
     }
@@ -71,6 +83,12 @@ impl CodecId {
     pub const fn to_wire(self) -> u8 {
         self as u8
     }
+
+    /// Returns true if this is an Opus variant.
+    pub const fn is_opus(self) -> bool {
+        matches!(self, Self::Opus6k | Self::Opus16k | Self::Opus24k
+            | Self::Opus32k | Self::Opus48k | Self::Opus64k)
+    }
 }
 
 /// Describes the complete quality configuration for a call session.
@@ -111,6 +129,30 @@ impl QualityProfile {
         frames_per_block: 8,
     };
 
+    /// Studio low: Opus 32kbps, minimal FEC.
+    pub const STUDIO_32K: Self = Self {
+        codec: CodecId::Opus32k,
+        fec_ratio: 0.1,
+        frame_duration_ms: 20,
+        frames_per_block: 5,
+    };
+
+    /// Studio: Opus 48kbps, minimal FEC.
+    pub const STUDIO_48K: Self = Self {
+        codec: CodecId::Opus48k,
+        fec_ratio: 0.1,
+        frame_duration_ms: 20,
+        frames_per_block: 5,
+    };
+
+    /// Studio high: Opus 64kbps, minimal FEC.
+    pub const STUDIO_64K: Self = Self {
+        codec: CodecId::Opus64k,
+        fec_ratio: 0.1,
+        frame_duration_ms: 20,
+        frames_per_block: 5,
+    };
+
     /// Estimated total bandwidth in kbps including FEC overhead.
     pub fn total_bitrate_kbps(&self) -> f32 {
         let base = self.codec.bitrate_bps() as f32 / 1000.0;