Add README, thread-safe engine, standalone format

README.md

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+# SM-26
+
+A simple subtractive synthesizer plugin built with JUCE / C++.
+
+* **VST3** + **Audio Unit** (macOS arm64), **VST3** (Linux)
+* 4 rotary knobs on the front panel whose meaning follows the selected preset
+* 52 factory presets (Bass / Lead / Pad / Keys / Pluck / FX / Stab / Arp)
+* tempo-synced delay (follows the host transport / BPM)
+* 4x80 HD44780-style pixel display with a cascaded on-screen menu
+* left/right/up/down navigation diamond + ENTER / ESC controls the menu
+* status footer with the git revision and local build time
+
+## Build
+
+Requires a C++17 compiler, CMake >= 3.22 and (on Linux) X11/ALSA dev headers.
+
+```sh
+make            # clones JUCE (once) into deps/ and builds
+make install    # installs + ad-hoc signs + un-quarantines
+make uninstall  # removes the installed plugins
+make distclean  # wipes build/
+```
+
+* macOS installs to `~/Library/Audio/Plug-Ins/` (AU + VST3).
+* Linux installs to `~/.vst3/`.
+
+If a freshly installed AU is not visible to `auval` / your DAW:
+
+```sh
+sudo killall -HUP coreaudiod
+```
+
+## Usage
+
+* Ship MIDI into the plugin; the 4 front-panel knobs drive whichever
+  parameters the current preset maps them to (e.g. cutoff/resonance/
+  envelope/delay, but many other routings exist).
+* **Nav diamond + ENTER/ESC** drive the on-screen menu:
+  * root menu -> PRESETS / OSCILLATORS / FILTER / ENVELOPE / DELAY / SYSTEM
+  * up/down = move, left/right = adjust value, ENTER = open/confirm, ESC = back
+* The LCD shows the current preset, the four knob mappings with live values,
+  host BPM and voice count. The delay can be set to a rhythmic subdivision
+  (SYNC) and locks to the host tempo.
+
+## Layout
+
+```
+Build: Makefile -> CMake -> JUCE (deps/juce)
+Source/
+  PluginProcessor.*   audio processor + DSP shell
+  SynthEngine.*       osc/filter/ADSR/delay voice engine
+  Presets.*           52 preset definitions + knob routings
+  SynthParams.*       parameter model + formatting
+  PluginEditor.*      panel, knobs, nav diamond, footer
+  LcdDisplay.*        4x80 HD44780-style display renderer
+  MenuSystem.*        cascaded menu state machine
+tools/gen_buildinfo.sh  generates git-version + build-time header
+```