Fix patch browser keyboard navigation to cover directory rows

Arrow keys now navigate the full virtual row list (../, subdirs, patches)
rather than only patch rows. Landing on a patch auto-loads it as before;
landing on .. or a subdir highlights it and Enter confirms navigation.
Added patchVCursor to UIState to track keyboard focus independently of
the loaded patch. Mouse-click on a patch now also syncs the cursor so
subsequent arrow-key movement starts from the right position.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

patches/Keys/Vibraphone.json

@@ -1,50 +0,0 @@
-{
-  "osc0_waveform": 0,
-  "osc0_dutyCycle": 0.500000,
-  "osc0_detune": 0.000000,
-  "osc0_gain": 4.000000,
-  "osc0_active": 1,
-  "osc0_octave": 0,
-  "osc0_modRouting0": 0,
-  "osc0_modRouting1": 3,
-  "osc0_modRouting2": 0,
-  "osc0_modDepth0": 0.000000,
-  "osc0_modDepth1": 10.000000,
-  "osc0_modDepth2": 0.000000,
-  "osc1_waveform": 0,
-  "osc1_dutyCycle": 0.500000,
-  "osc1_detune": 2.000000,
-  "osc1_gain": 0.300000,
-  "osc1_active": 1,
-  "osc1_octave": 1,
-  "osc1_modRouting0": 0,
-  "osc1_modRouting1": 0,
-  "osc1_modRouting2": 2,
-  "osc1_modDepth0": 0.000000,
-  "osc1_modDepth1": 0.000000,
-  "osc1_modDepth2": 1.500000,
-  "ampEnv_attack": 0.001000,
-  "ampEnv_decay": 2.000000,
-  "ampEnv_sustain": 0.000000,
-  "ampEnv_release": 0.600000,
-  "modEnv_attack": 0.001000,
-  "modEnv_decay": 0.080000,
-  "modEnv_sustain": 0.000000,
-  "modEnv_release": 0.040000,
-  "lfo0_rate": 4.500000,
-  "lfo0_waveform": 0,
-  "lfo0_active": 1,
-  "lfo1_rate": 1.000000,
-  "lfo1_waveform": 0,
-  "lfo1_active": 0,
-  "filter_cutoff": 10000.000000,
-  "filter_resonance": 0.100000,
-  "filter_type": 0,
-  "filter_active": 1,
-  "filter_modRouting": 0,
-  "filter_modDepth": 0.000000,
-  "filter_resModRouting": 0,
-  "filter_resModDepth": 0.000000,
-  "master_volume": 0.800000,
-  "master_pitchBendRange": 2.000000
-}