feat: flexible Whisper installation options for different system configurations (#63)

* fix: VOSK-only install and CLI arg handling for low-memory systems

Fixes several issues reported by users on low-memory systems (8GB RAM):

1. Install script: Don't auto-install Whisper in non-interactive mode
   - Previously, running 'curl | bash' would install Whisper by default
   - Now requires explicit --with-whisper flag to install Whisper
   - Prevents OOM errors on systems with limited RAM

2. CLI arguments: Command-line flags now properly override saved config
   - --engine vosk now works even if config file has whisper set
   - --model flag also properly overrides saved model setting
   - Checks sys.argv to detect if user explicitly provided arguments

3. Default engine: Changed from 'whisper' to 'vosk'
   - VOSK works on low-memory systems without OOM issues
   - Users can still install and use Whisper with --with-whisper flag
   - Existing configs with 'whisper' engine are still respected

Reported issues:
- OOM during installation on 8GB RAM system
- vocalinux --engine vosk being ignored
- Config file not respected when trying to force VOSK

* fix: keep whisper as default engine, improve test robustness

- Reverted default engine back to 'whisper' for better accuracy
- Install script still defaults to VOSK-only install (--with-whisper for Whisper)
- CLI args still properly override saved config
- Improved test_config_manager tests to handle module caching issues

* fix: default to Whisper install, --no-whisper for VOSK-only on low-RAM systems

Updated install behavior:
- Default (curl|bash): Installs Whisper for best experience
- --no-whisper flag: Skips Whisper AND creates config with VOSK as default engine

This allows low-RAM users (8GB) to run:
  curl -fsSL .../install.sh | bash -s -- --no-whisper

Which will:
1. Skip installing torch/whisper (avoids OOM)
2. Create ~/.config/vocalinux/config.json with engine='vosk'
3. App will use VOSK by default without needing CLI flags

* docs: clarify --no-whisper is for low-RAM systems (8GB or less)

Updated README and website to explain that --no-whisper flag:
- Is intended for systems with 8GB RAM or less
- Avoids out-of-memory errors during installation
- Configures VOSK as the default speech recognition engine

* feat: add --whisper-cpu flag for CPU-only PyTorch installation

New installation option for users without NVIDIA GPU or with limited RAM:

Install script changes:
- Added --whisper-cpu flag: Installs CPU-only PyTorch (~200MB vs ~2.3GB)
- Uses https://download.pytorch.org/whl/cpu index for smaller torch package
- Interactive mode now offers 3 options: GPU, CPU-only, or skip Whisper
- Updated help text to explain all Whisper installation options

Documentation updates:
- README: Added --whisper-cpu example with explanation
- Website: Added new 'Whisper CPU-only' install option section

Installation options summary:
- Default (curl|bash): Whisper + GPU/CUDA support (~2.3GB, 5-10 min)
- --whisper-cpu: Whisper + CPU-only PyTorch (~200MB, 3-4 min)
- --no-whisper: VOSK only, no Whisper (~2-3 min)

web/src/app/page.tsx

@@ -43,6 +43,10 @@ const oneClickInstallCommand = `curl \\
   -fsSL https://raw.githubusercontent.com/jatinkrmalik/vocalinux/main/install.sh \\
   | bash`;
 
+const oneClickInstallWhisperCpu = `curl \\
+  -fsSL https://raw.githubusercontent.com/jatinkrmalik/vocalinux/main/install.sh \\
+  | bash -s -- --whisper-cpu`;
+
 const oneClickInstallNoWhisper = `curl \\
   -fsSL https://raw.githubusercontent.com/jatinkrmalik/vocalinux/main/install.sh \\
   | bash -s -- --no-whisper`;
@@ -603,16 +607,43 @@ export default function HomePage() {
                   </div>
                 </div>
 
-                {/* Alternative install */}
+                {/* Alternative install - CPU only */}
                 <div className="border-t border-zinc-200 dark:border-zinc-700 pt-6">
                   <div className="flex items-center gap-3 mb-4">
                     <div className="bg-blue-500/10 p-2 rounded-lg">
-                      <Zap className="h-5 w-5 text-blue-500" />
+                      <Cpu className="h-5 w-5 text-blue-500" />
                     </div>
                     <div className="flex-1">
-                      <h3 className="text-lg font-semibold">Quick Install (VOSK only)</h3>
+                      <h3 className="text-lg font-semibold">Whisper CPU-only</h3>
                       <p className="text-sm text-muted-foreground">
-                        Faster install, lighter on resources (~2-3 min)
+                        Smaller download (~200MB vs ~2.3GB) - no NVIDIA GPU needed (~3-4 min)
+                      </p>
+                    </div>
+                    <CopyButton text={oneClickInstallWhisperCpu} />
+                  </div>
+                  <div className="overflow-x-auto">
+                    <SyntaxHighlighter
+                      language="bash"
+                      style={atomOneDark}
+                      className="rounded-lg text-sm"
+                      customStyle={{ margin: 0, maxWidth: '100%', overflowX: 'auto' }}
+                      wrapLongLines={false}
+                    >
+                      {oneClickInstallWhisperCpu}
+                    </SyntaxHighlighter>
+                  </div>
+                </div>
+
+                {/* Alternative install - VOSK only */}
+                <div className="border-t border-zinc-200 dark:border-zinc-700 pt-6">
+                  <div className="flex items-center gap-3 mb-4">
+                    <div className="bg-green-500/10 p-2 rounded-lg">
+                      <Zap className="h-5 w-5 text-green-500" />
+                    </div>
+                    <div className="flex-1">
+                      <h3 className="text-lg font-semibold">VOSK only (lightest)</h3>
+                      <p className="text-sm text-muted-foreground">
+                        For low-RAM systems (8GB or less) - skips Whisper entirely (~2-3 min)
                       </p>
                     </div>
                     <CopyButton text={oneClickInstallNoWhisper} />