docs: fix .cursor/ helper docs

The .cursor/ directory holds the dev-side helper docs that Cursor and
contributors using AI tooling rely on to bootstrap plugin development.
Several of them had the same bug patterns as the user-facing docs.

.cursor/plugin_templates/QUICK_START.md
- "Adding Image Rendering" section showed
  display_manager.draw_image(image, x=0, y=0). That method doesn't
  exist on DisplayManager (same bug as PLUGIN_API_REFERENCE.md and
  PLUGIN_DEVELOPMENT_GUIDE.md). Replaced with the canonical
  display_manager.image.paste((x,y)) pattern, including the
  transparency-mask form.

.cursor/plugins_guide.md
- 10 occurrences of ./dev_plugin_setup.sh — the script lives at
  scripts/dev/dev_plugin_setup.sh, so anyone copy-pasting these
  examples gets "command not found". Bulk fixed via sed.
- "Test with emulator: python run.py --emulator" — there's no
  --emulator flag. Replaced with the real options:
  EMULATOR=true python3 run.py for the full display, or
  scripts/dev_server.py for the dev preview.
- Secrets management section showed a fictional
  "config_secrets": { "api_key": "my-plugin.api_key" } reference
  field. Verified in src/config_manager.py:162-172 that secrets are
  loaded by deep-merging config_secrets.json into the main config.
  There is no separate reference field — just put the secret under
  the same plugin namespace and read it from the merged config.
  Rewrote the section with the real pattern.
- "ssh pi@raspberrypi" -> "ssh ledpi@your-pi-ip" (consistent with
  the rest of LEDMatrix docs which use ledpi as the default user)

.cursor/README.md
- Same ./dev_plugin_setup.sh -> ./scripts/dev/dev_plugin_setup.sh
  fix (×6 occurrences via replace_all).
- Same "python run.py --emulator" -> "EMULATOR=true python3 run.py"
  fix. Also added a pointer to scripts/dev_server.py for previewing
  plugins without running the full display.
- "Example Plugins: plugins/hockey-scoreboard/" — the canonical
  source is the ledmatrix-plugins repo. Installed copies land in
  plugin-repos/ or plugins/. Updated the line to point at the
  ledmatrix-plugins repo and explain both local locations.

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

.cursor/README.md

@@ -43,39 +43,46 @@ cp ../../.cursor/plugin_templates/*.template .
 2. **Using dev_plugin_setup.sh**:
 ```bash
 # Link from GitHub
-./dev_plugin_setup.sh link-github my-plugin
+./scripts/dev/dev_plugin_setup.sh link-github my-plugin
 
 # Link local repo
-./dev_plugin_setup.sh link my-plugin /path/to/repo
+./scripts/dev/dev_plugin_setup.sh link my-plugin /path/to/repo
 ```
 
-### Running Plugins
+### Running the Display
 
 ```bash
-# Emulator (development)
-python run.py --emulator
+# Emulator mode (development, no hardware required)
+EMULATOR=true python3 run.py
 
-# Hardware (production)
-python run.py
+# Hardware (production, requires the rpi-rgb-led-matrix submodule built)
+python3 run.py
 
-# As service
+# As a systemd service
 sudo systemctl start ledmatrix
+
+# Dev preview server (renders plugins to a browser without running run.py)
+python3 scripts/dev_server.py  # then open http://localhost:5001
 ```
 
+There is no `--emulator` flag — the emulator is selected via the
+`EMULATOR=true` environment variable, which `src/display_manager.py:2`
+checks at import time.
+
 ### Managing Plugins
 
 ```bash
 # List plugins
-./dev_plugin_setup.sh list
+./scripts/dev/dev_plugin_setup.sh list
 
 # Check status
-./dev_plugin_setup.sh status
+./scripts/dev/dev_plugin_setup.sh status
 
 # Update plugin(s)
-./dev_plugin_setup.sh update [plugin-name]
+./scripts/dev/dev_plugin_setup.sh update [plugin-name]
 
 # Unlink plugin
-./dev_plugin_setup.sh unlink <plugin-name>
+./scripts/dev/dev_plugin_setup.sh unlink <plugin-name>
 ```
 
 ## Using These Files with Cursor
@@ -118,9 +125,13 @@ Refer to `plugins_guide.md` for:
 - **Plugin System**: `src/plugin_system/`
 - **Base Plugin**: `src/plugin_system/base_plugin.py`
 - **Plugin Manager**: `src/plugin_system/plugin_manager.py`
-- **Example Plugins**: `plugins/hockey-scoreboard/`, `plugins/football-scoreboard/`
+- **Example Plugins**: see the
+  [`ledmatrix-plugins`](https://github.com/ChuckBuilds/ledmatrix-plugins)
+  repo for canonical sources (e.g. `plugins/hockey-scoreboard/`,
+  `plugins/football-scoreboard/`). Installed plugins land in
+  `plugin-repos/` (default) or `plugins/` (dev fallback).
 - **Architecture Docs**: `docs/PLUGIN_ARCHITECTURE_SPEC.md`
-- **Development Setup**: `dev_plugin_setup.sh`
+- **Development Setup**: `scripts/dev/dev_plugin_setup.sh`
 
 ## Getting Help