Docs: Fix TangentialArc example and add quadrant visualization (codeberg-mirror/#1)

## Overview: What does this pull request change?
This PR fixes the documentation for `TangentialArc`.
1. It replaces the static code block in the `TangentialArc` example with the `.. manim::` directive, allowing the example image/video to actually render in the documentation.
2. It adds a new second example scene, `TangentialArcCorners`, which visually demonstrates how the `corner` parameter (e.g., `(1,1)`, `(-1,1)`) affects the arc's orientation.

## Motivation and Explanation: Why and how do your changes improve the library?
Previously, the `TangentialArc` example was hidden inside a standard code block, so users could not see what the output looked like.
Additionally, the `corner` parameter is complex to visualize mentally. The new `TangentialArcCorners` scene provides a clear visual reference for all four possible quadrant configurations, making the class much easier to learn.

## Links to added or changed documentation pages
N/A

## Further Information and Comments
I have tested these changes locally and verified that the images generate correctly.
I am submitting this to the Codeberg mirror as per the current guidance regarding the GitHub incident.

**Visual Proof of the new example:**
I have attached the image

## Reviewer Checklist
- [ ] The PR title is descriptive enough for the changelog, and the PR is labeled correctly
- [ ] If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
- [ ] If applicable: newly added functions and classes are tested

Reviewed-on: https://codeberg.org/ManimCommunity/manim/pulls/1
Reviewed-by: Benjamin Hackl <behackl@noreply.codeberg.org>
Co-authored-by: TahaShams <01-134222-153@student.bahria.edu.pk>
Co-committed-by: TahaShams <01-134222-153@student.bahria.edu.pk>

manim/mobject/geometry/arc.py

@@ -505,9 +505,10 @@ class TangentialArc(ArcBetweenPoints):
     You can choose any of the 4 possible corner arcs via the `corner` tuple.
     corner = (s1, s2) where each si is ±1 to control direction along each line.
 
-        Example
-    -------
+    Examples
+    --------
     .. manim:: TangentialArcExample
+        :save_last_frame:
 
         class TangentialArcExample(Scene):
             def construct(self):
@@ -518,6 +519,32 @@ class TangentialArc(ArcBetweenPoints):
 
                 arc = TangentialArc(line1, line2, radius=2.25, corner=(1, 1), color=TEAL)
                 self.add(arc, line1, line2)
+
+    The following example shows all four possible corner configurations:
+
+    .. manim:: TangentialArcCorners
+        :save_last_frame:
+
+        class TangentialArcCorners(Scene):
+            def construct(self):
+                # Create two intersecting lines
+                line1 = DashedLine(start=3 * LEFT, end=3 * RIGHT, color=GREY)
+                line2 = DashedLine(start=3 * UP, end=3 * DOWN, color=GREY)
+
+                # All four corner configurations with different colors
+                arc_pp = TangentialArc(line1, line2, radius=1.5, corner=(1, 1), color=RED)
+                arc_pn = TangentialArc(line1, line2, radius=1.5, corner=(1, -1), color=GREEN)
+                arc_np = TangentialArc(line1, line2, radius=1.5, corner=(-1, 1), color=BLUE)
+                arc_nn = TangentialArc(line1, line2, radius=1.5, corner=(-1, -1), color=YELLOW)
+
+                # Labels for each arc
+                label_pp = Text("(1,1)", font_size=24, color=RED).next_to(arc_pp, UR, buff=0.1)
+                label_pn = Text("(1,-1)", font_size=24, color=GREEN).next_to(arc_pn, DR, buff=0.1)
+                label_np = Text("(-1,1)", font_size=24, color=BLUE).next_to(arc_np, UL, buff=0.1)
+                label_nn = Text("(-1,-1)", font_size=24, color=YELLOW).next_to(arc_nn, DL, buff=0.1)
+
+                self.add(line1, line2, arc_pp, arc_pn, arc_np, arc_nn)
+                self.add(label_pp, label_pn, label_np, label_nn)
     """
 
     def __init__(