fix(extended-thinking): correct fictional /think command to valid ultrathink keyword (#83)

- Replace fictional `/think` example with official `ultrathink` keyword
- Fix Q4 options: `/think` → `/effort max`, `--thinking` → `ultrathink`
- Fix Q5: correct the answer that "ultrathink" DOES trigger deep reasoning
- Sync changes across English, Ukrainian, and Vietnamese translations

Background: `/think` is not a valid slash command in Claude Code (verified
against official commands reference at code.claude.com/docs/en/commands).
The correct way to trigger deep reasoning for a single response is to
include "ultrathink" in the prompt.

Sources:
- https://code.claude.com/docs/en/commands (no /think command exists)
- https://code.claude.com/docs/en/model-config (ultrathink is valid keyword)

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

.claude/skills/lesson-quiz/references/question-bank.md

@@ -704,18 +704,18 @@
 
 ### Q4
 - **Category**: practical
-- **Question**: How do you toggle extended thinking during a session?
-- **Options**: A) Type `/think` | B) Press `Option+T` (macOS) or `Alt+T` | C) Use `--thinking` flag | D) It's always enabled and cannot be toggled
+- **Question**: How do you toggle extended thinking visibility during a session?
+- **Options**: A) Type `/effort max` | B) Press `Option+T` (macOS) or `Alt+T` | C) Include "ultrathink" in prompt | D) It's always visible and cannot be toggled
 - **Correct**: B
-- **Explanation**: Option+T (macOS) or Alt+T toggles extended thinking. It's enabled by default for all models. Opus 4.6 supports adaptive effort levels.
+- **Explanation**: Option+T (macOS) or Alt+T toggles extended thinking visibility. For one-off deep reasoning, include "ultrathink" in your prompt; for session-level control, use `/effort` command.
 - **Review**: Extended Thinking section
 
 ### Q5
 - **Category**: conceptual
-- **Question**: Are "think" or "ultrathink" special keywords that activate enhanced thinking?
-- **Options**: A) Yes, they activate deeper reasoning | B) No, they are treated as regular prompt text with no special behavior | C) Only "ultrathink" is special | D) They work only with Opus
-- **Correct**: B
-- **Explanation**: The documentation explicitly states these are regular prompt instructions, not special activation keywords. Extended thinking is controlled via Alt+T toggle and environment variables.
+- **Question**: Does the "ultrathink" keyword trigger deep reasoning?
+- **Options**: A) Yes, it triggers deep reasoning for one response without changing session settings | B) No, it's treated as regular prompt text | C) Yes, but only on Opus 4.6 | D) Yes, and it permanently changes the effort level
+- **Correct**: A
+- **Explanation**: Including "ultrathink" in your prompt adds an in-context instruction for the model to reason more on that turn. It does not change the effort level sent to the API—use `/effort max` for session-level deep reasoning.
 - **Review**: Extended Thinking section
 
 ### Q6

09-advanced-features/README.md

@@ -318,7 +318,7 @@ claude --effort high "complex architectural review"
 ### Example: Architectural Decision
 
 ```
-User: /think Should we use microservices or a monolith for our e-commerce platform?
+User: ultrathink Should we use microservices or a monolith for our e-commerce platform?
 
 Claude: Let me think through this architectural decision carefully...
 

uk/09-advanced-features/README.md

@@ -262,7 +262,7 @@ claude --effort high "complex architectural review"
 ### Приклад: Архітектурне рішення
 
 ```
-User: /think Should we use microservices or a monolith for our e-commerce platform?
+User: ultrathink Should we use microservices or a monolith for our e-commerce platform?
 
 Claude: Let me think through this architectural decision carefully...
 

vi/09-advanced-features/README.md

@@ -257,7 +257,7 @@ claude --effort high "complex architectural review"
 ### Example: Architectural Decision
 
 ```
-User: /think Should we use microservices or a monolith for our e-commerce platform?
+User: ultrathink Should we use microservices or a monolith for our e-commerce platform?
 
 Claude: Let me think through this architectural decision carefully...