Implement the three missing architectural components of the Output Rendering
Framework as specified in issue #917:

1. RendererRegistry (spec §27249-27350): Central registry for format
   (MaterializationStrategy, ElementRenderer) pairs with register(),
   resolve(), available_formats(), is_registered() methods and a
   FormatRegistration model. Built-in formats pre-registered in
   default_registry. Replaces hardcoded if/elif chains for format
   resolution.

2. ElementRenderer Protocol (spec §26557-26654): Per-element render
   methods (render_panel, render_table, render_tree, etc.) plus
   serialize() and can_render(). Six concrete implementations:
   PlainElementRenderer, ColorElementRenderer, TableElementRenderer,
   RichElementRenderer, JsonElementRenderer, YamlElementRenderer.
   Each format now has a paired (Strategy, Renderer).

3. TerminalCapabilities (spec §27264-27301): Extended from 4 fields to
   all 11 spec-defined fields: width, height, supports_256_color,
   supports_truecolor, supports_unicode, supports_alternate_screen,
   no_color, plus renames supports_cursor → supports_cursor_movement,
   term → term_program. Backward-compatible properties preserved.

Additional fixes:
- ColumnDef serialises column type as 'type' (not 'col_type') per spec
  §26199, with alias for backward compatibility
- YAML output uses sort_keys=True per spec §27168
- Progress elements omitted from JSON/YAML per spec §26936
- MaterializationStrategy.bind(renderer, terminal_caps) method added
  to protocol and all strategy implementations (SD-19 resolved)
- Updated SD documentation in __init__.py

ISSUES CLOSED: #917

@@ -0,0 +1,678 @@
+"""RendererRegistry and ElementRenderer protocol for the output framework.

@@ -0,0 +106,4 @@
+
+    def render_table(self, table: Table) -> str:
+        return ""  # pragma: no cover
+

@@ -0,0 +127,4 @@
+
+    def render_separator(self, separator: Separator) -> str:
+        return ""  # pragma: no cover
+

@@ -89,6 +89,13 @@ class MaterializationStrategy(Protocol):
 
     def on_session_end(self, event: SessionEnd) -> None: ...  # pragma: no cover
 
+    def bind(

@@ -0,0 +145,4 @@
+            Separator: self.render_separator,
+            ActionHint: self.render_action_hint,
+        }
+        handler = dispatch.get(type(element))

@@ -0,0 +173,4 @@
+    def render_panel(self, panel: Panel) -> str:
+        from cleveragents.cli.output._renderers import render_element_plain
+
+        return render_element_plain(panel)

@@ -0,0 +555,4 @@
+                given terminal capabilities.
+            fallback: Optional fallback format name if this format cannot
+                operate in the current terminal environment.
+        """

@@ -89,6 +89,13 @@ class MaterializationStrategy(Protocol):
 
     def on_session_end(self, event: SessionEnd) -> None: ...  # pragma: no cover
 
+    def bind(

@@ -0,0 +1,678 @@
+"""RendererRegistry and ElementRenderer protocol for the output framework.

@@ -0,0 +152,4 @@
+
+    def serialize(self, output: StructuredOutput) -> str:
+        """Serialize a complete StructuredOutput by rendering each element."""
+        buf = StringIO()

@@ -0,0 +192,4 @@
+
+    def render_progress(self, progress: ProgressIndicator) -> str:
+        from cleveragents.cli.output._renderers import render_element_plain
+

@@ -0,0 +307,4 @@
+        from cleveragents.cli.output._boxdraw import render_element_table
+
+        return render_element_table(status)
+

@@ -89,6 +89,13 @@ class MaterializationStrategy(Protocol):
 
     def on_session_end(self, event: SessionEnd) -> None: ...  # pragma: no cover
 
+    def bind(

@@ -0,0 +1,678 @@
+"""RendererRegistry and ElementRenderer protocol for the output framework.

@@ -0,0 +140,4 @@
+            StatusMessage: self.render_status,
+            ProgressIndicator: self.render_progress,
+            CodeBlock: self.render_code,
+            DiffBlock: self.render_diff,

@@ -0,0 +171,4 @@
+    format_name: str = "plain"
+
+    def render_panel(self, panel: Panel) -> str:
+        from cleveragents.cli.output._renderers import render_element_plain

@@ -0,0 +280,4 @@
+        return render_element_color(hint)
+
+    def can_render(self, terminal_caps: TerminalCapabilities) -> bool:
+        return terminal_caps.supports_ansi

@@ -0,0 +553,4 @@
+                given terminal capabilities.
+            renderer_factory: Callable that creates an ElementRenderer,
+                given terminal capabilities.
+            fallback: Optional fallback format name if this format cannot