fix(tui): fix Throbber Rejects Invalid Styles test indentation and add CHANGELOG entry

Use Fix Python Indentation + temp file in robot/tui_throbber.robot to correctly
reconstruct indentation stripped by Robot Framework's Catenate keyword in the
Throbber Rejects Invalid Styles test case. Add indentation_library.py to the
suite's Library imports. Add CHANGELOG.md fix entry for #6357.

ISSUES CLOSED: #6357

CHANGELOG.md

@@ -50,6 +50,16 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Fixed
 
+- **LoadingThrobber Widget Restored** (#6357): Restored `LoadingThrobber` widget
+  (`src/cleveragents/tui/widgets/throbber.py`) and its Robot Framework integration
+  tests (`robot/tui_throbber.robot`) that were missing from master. Also restored
+  supporting modules `src/cleveragents/tui/quotes.py` and
+  `src/cleveragents/tui/data/throbber_quotes.txt`. Fixed the `Throbber Rejects
+  Invalid Styles` integration test by using `Fix Python Indentation` to correctly
+  reconstruct indentation stripped by Robot Framework's `Catenate` keyword.
+  Narrowed exception handling in `throbber.py` to specific types
+  (`ImportError`, `AttributeError`) per coding standards.
+
 - **Built-in actors v3 YAML format** (#10883): Fixed `agents actor run` failing for
   built-in actors (e.g., `openai/gpt-4`, `anthropic/claude-3-opus`) due to missing
   v3 `type` field in stored configuration. `ActorRegistry.ensure_built_in_actors()`

robot/tui_throbber.robot

@@ -4,6 +4,7 @@ Test Tags        tui    throbber    widget
 Resource         ${CURDIR}/common.resource
 Library          Process
 Library          Collections
+Library          indentation_library.py
 Suite Setup      Setup Test Environment With Database Isolation
 Suite Teardown   Cleanup Test Environment
 
@@ -69,6 +70,10 @@ Throbber Rejects Invalid Styles
     ...        print("throbber-invalid-style-ok")
     ...    else:
     ...        raise AssertionError("Expected ValueError for invalid throbber style")
-    ${result}=    Run Process    ${PYTHON}    -c    ${script}    shell=False    timeout=120s    on_timeout=kill
+    ${code}=    Fix Python Indentation    ${script}
+    ${temp_file}=    Evaluate    (lambda t: (__import__('os').close(t[0]), t[1])[-1])(__import__('tempfile').mkstemp(suffix='.py', dir='/tmp'))
+    Create File    ${temp_file}    ${code}
+    ${result}=    Run Process    ${PYTHON}    ${temp_file}    shell=False    timeout=120s    on_timeout=kill
+    Remove File    ${temp_file}
     Should Be Equal As Integers    ${result.rc}    0
     Should Contain    ${result.stdout}    throbber-invalid-style-ok