Add Bank 12: Blues genre presets — SRV, Muddy/Buddy, B.B. King, Gary Moore

Bank 12 (Blues) with 4 factory presets covering 9 legendary blues artists:
- Preset 0: Texas Flood (SRV) — TS808 + Fender Super Reverb
- Preset 1: Mannish Boy (Muddy Waters) — Fender Bassman cranked w/ slapback
- Preset 2: The Thrill (B.B. King) — Twin Reverb clean w/ comp
- Preset 3: Still Got the Blues (Gary Moore) — Marshall crunch w/ delay

Includes docs/blues-genre-research.md with full gear deep-dives, NAM
model sourcing guide (Tone3000 URLs), chain architectures, and
parameter value rationale for all 9 artists (SRV, B.B. King, Albert King,
Freddie King, Muddy Waters, Buddy Guy, Gary Moore, Joe Bonamassa,
John Mayer).

presets/factory/bank_12/preset_1.json

@@ -0,0 +1,57 @@
+{
+  "name": "Blues — Mannish Boy (Muddy Waters)",
+  "bank": 12,
+  "program": 1,
+  "master_volume": 0.85,
+  "chain": [
+    {
+      "fx_type": "noise_gate",
+      "enabled": true,
+      "bypass": false,
+      "params": { "threshold": 0.01 },
+      "nam_model_path": "",
+      "ir_file_path": ""
+    },
+    {
+      "fx_type": "boost",
+      "enabled": true,
+      "bypass": false,
+      "params": { "gain_db": 6.0 },
+      "nam_model_path": "",
+      "ir_file_path": ""
+    },
+    {
+      "fx_type": "nam_amp",
+      "enabled": true,
+      "bypass": false,
+      "params": { "level": 0.8 },
+      "nam_model_path": "/root/.pedal/models/Magnatone_Super59_Pushed.nam",
+      "ir_file_path": ""
+    },
+    {
+      "fx_type": "ir_cab",
+      "enabled": true,
+      "bypass": false,
+      "params": { "wet": 1.0, "dry": 0.0 },
+      "nam_model_path": "",
+      "ir_file_path": "/root/.pedal/irs/jazz-1x15.wav"
+    },
+    {
+      "fx_type": "delay",
+      "enabled": true,
+      "bypass": false,
+      "params": { "time": 150.0, "feedback": 0.15, "mix": 0.25 },
+      "nam_model_path": "",
+      "ir_file_path": ""
+    },
+    {
+      "fx_type": "volume",
+      "enabled": true,
+      "bypass": false,
+      "params": { "level": 0.88 },
+      "nam_model_path": "",
+      "ir_file_path": ""
+    }
+  ],
+  "midi_mappings": {}
+}