Delegate diff rendering wholesale to termflow 0.3.0

Diff parsing, syntax highlighting, backgrounds, and theme tints now live
in termflow.diff; tools/common.py keeps only thin adapters. Deleted the
pygments machinery (TOKEN_COLORS, EXTENSION_TO_LEXER_NAME,
_get_lexer_for_extension, _get_token_color, _highlight_code_line,
_extract_file_extension_from_diff, _format_diff_with_syntax_highlighting,
PYGMENTS_AVAILABLE) — ~350 lines gone, and language detection upgraded
for free via termflow's LANGUAGE_ALIASES.

Adapters: _termflow_diff_renderer wires the termflow_highlighter theme
callback (diff_line_tints contract preserved) plus the user's configured
/diff colors; format_diff_with_colors keeps its signature (block mode,
Text.from_ansi) so diff-menu previews are untouched; new
stream_diff_ansi_lines yields rendered ANSI lines incrementally via
termflow's DiffStream, and rich_renderer._render_diff now prints diffs
progressively line-by-line instead of one monolithic Text block.

Author: mpfaffenberger

code_puppy/messaging/rich_renderer.py

@@ -25,7 +25,7 @@
     get_suppress_informational_messages,
     get_suppress_thinking_messages,
 )
-from code_puppy.tools.common import format_diff_with_colors
+from code_puppy.tools.common import stream_diff_ansi_lines
 from code_puppy.tools.subagent_context import is_subagent
 
 from .bus import MessageBus
@@ -870,7 +870,7 @@ def _render_diff(self, msg: DiffMessage) -> None:
         if not msg.diff_lines:
             return
 
-        # Reconstruct unified diff text from diff_lines for format_diff_with_colors
+        # Reconstruct unified diff text from diff_lines for termflow's renderer
         diff_text_lines = []
         for line in msg.diff_lines:
             if line.type == "add":
@@ -887,9 +887,13 @@ def _render_diff(self, msg: DiffMessage) -> None:
 
         diff_text = "\n".join(diff_text_lines)
 
-        # Use the beautiful syntax-highlighted diff formatter
-        formatted_diff = format_diff_with_colors(diff_text)
-        self._console.print(formatted_diff)
+        # Stream through termflow's diff renderer: each line paints as soon
+        # as it renders, so big diffs appear progressively instead of
+        # blocking on one monolithic block.
+        from rich.text import Text
+
+        for ansi_line in stream_diff_ansi_lines(diff_text):
+            self._console.print(Text.from_ansi(ansi_line))
 
     # =========================================================================
     # Shell Output