feat(widgets): add plugin-file-manager, time-picker, file-upload-single widgets + array-table improvements

## New widgets

### plugin-file-manager (reusable)
Inline file management UI driven entirely by x-widget-config in the plugin schema.
Any plugin can adopt it by declaring web_ui_actions in manifest.json and adding
x-widget: "plugin-file-manager" to their config schema.

Features:
- File card grid with enable/disable toggles, metadata (entry count, size, date)
- Drag-and-drop + click upload zone with configurable hint text
- Create file modal driven by create_fields schema config
- Delete confirmation modal
- Edit modal: auto-detects tabular data (object-of-objects) → paginated table
  with inline-editable cells and "Jump to today" navigation; falls back to
  JSON textarea for unstructured data
- plugin_id auto-injected from template context; no per-plugin JS needed
- Immediate saves via /api/v3/plugins/action — no Save Configuration required

### time-picker
Wraps native <input type="time">, returns HH:MM string. Generic, zero config.

### file-upload-single
Single-image upload for string fields. Shows thumbnail preview + clear button.
plugin_id auto-injected from template context.

## New route (pages_v3.py)
GET /v3/plugin-ui/<plugin_id>/web-ui/<filename>
Serves a plugin's web_ui/ HTML fragment as a standalone page, wrapping it with
a minimal HTML page that injects window.PLUGIN_ID and loads Tailwind CSS.
Enables the json-file-manager iframe fallback (Phase A) and future plugin UIs.

## plugin_config.html updates
- json-file-manager: renders plugin's web_ui/file_manager.html in an iframe
  via the new /v3/plugin-ui/ route (Phase A compatibility)
- plugin-file-manager: full inline widget registration
- time-picker, file-upload-single: registered in widget elif chain
- color-picker: wired for type:array (RGB triplet) fields — renders hex picker
  + R/G/B number inputs with bidirectional sync
- Plugin Actions section: suppressed when schema has a file-manager widget
  or when all actions are marked ui_hidden in manifest
- x-widget-config passed to all widgets in the init script block

## array-table.js improvements (v2.0.0)
- enum fields → <select> dropdown instead of plain text
- date-picker x-widget → <input type=date>
- time-picker x-widget → <input type=time>
- file-upload-single x-widget → path input + upload button + thumbnail
- Row edit modal (⚙) for non-displayed nested properties (layout, style objects)
  with color pickers, enum selects, number inputs
- getValue() collects <select> values and nested key paths
- Inline image upload via handleArrayTableImageUpload()

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

docs/widget-guide.md

@@ -10,6 +10,98 @@ The LEDMatrix Widget Registry system allows plugins to use reusable UI component
 
 ## Available Core Widgets
 
+### Plugin File Manager Widget (`plugin-file-manager`)
+
+Full inline file management UI for plugins that manage files via the `web_ui_actions` system. Renders a card grid, upload zone, create/delete modals, and an entry table editor — entirely inline, no iframe.
+
+`plugin_id` is **automatically injected** from template context. File operations call `/api/v3/plugins/action` immediately on user action; no Save Configuration needed.
+
+**Schema Configuration:**
+```json
+{
+  "file_manager": {
+    "type": "null",
+    "title": "Data Files",
+    "x-widget": "plugin-file-manager",
+    "x-widget-config": {
+      "actions": {
+        "list":   "list-files",
+        "get":    "get-file",
+        "save":   "save-file",
+        "upload": "upload-file",
+        "delete": "delete-file",
+        "create": "create-file",
+        "toggle": "toggle-category"
+      },
+      "upload_hint":      "JSON files with day numbers 1–365 as keys",
+      "directory_label":  "my_data/",
+      "create_fields": [
+        { "key": "category_name", "label": "Category Name",
+          "placeholder": "e.g., my_words", "pattern": "^[a-z0-9_]+$",
+          "hint": "Lowercase letters, numbers, underscores" },
+        { "key": "display_name", "label": "Display Name",
+          "placeholder": "e.g., My Words", "hint": "Optional" }
+      ]
+    }
+  }
+}
+```
+
+Not all 7 actions are required — omit any key to hide the corresponding UI element (e.g., no `create` = no New File button, no `toggle` = no enable/disable switch).
+
+The edit view auto-detects whether file content is tabular (object-of-objects with uniform keys) and shows a paginated table editor with inline cells. Otherwise falls back to a JSON textarea.
+
+**Used by:** of-the-day
+
+---
+
+### Time Picker Widget (`time-picker`)
+
+Single time selection using the browser's native time input. Returns a string in `HH:MM` (24-hour) format. Generic — works in any plugin without configuration.
+
+**Schema Configuration:**
+```json
+{
+  "target_time": {
+    "type": "string",
+    "x-widget": "time-picker",
+    "default": "00:00",
+    "x-options": {
+      "placeholder": "Select time",
+      "clearable": true
+    }
+  }
+}
+```
+
+**Used by:** countdown
+
+---
+
+### File Upload Single Widget (`file-upload-single`)
+
+Single-image upload for string fields. Uploads to the plugin's asset folder (`assets/plugins/<plugin_id>/uploads/`) and sets the string field value to the returned relative path. Shows a thumbnail preview and a clear button. The `plugin_id` is **automatically injected** from the template context — no need to specify it in the schema.
+
+**Schema Configuration:**
+```json
+{
+  "image_path": {
+    "type": "string",
+    "x-widget": "file-upload-single",
+    "x-upload-config": {
+      "allowed_types": ["image/png", "image/jpeg", "image/bmp", "image/gif"],
+      "max_size_mb": 5
+    }
+  }
+}
+```
+
+Note: Unlike `file-upload` (array-level), this widget is for a single `string` field. It is ideal for per-item images inside `array-table` rows.
+
+**Used by:** countdown
+
+---
+
 ### File Upload Widget (`file-upload`)
 
 Upload and manage image files with drag-and-drop support, preview, delete, and scheduling.