Add multilingual Agila learning examples and Git practice guide

en/flying-v-validation-and-capstone/README.md

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+# An explainable Agila study-app prototype
+
+Prepare a reviewable Flying V prototype using documented lifecycle and UI contracts. Add a separate descriptor-validation experiment; document what the sandbox establishes and what needs a production runtime.
+
+- Explain all retained APIs with references to the public SDK.
+- Include one successful lifecycle and one handled failure case.
+- Include a UI description and accurate expected sandbox output.
+- Test valid, zero, and negative mesh counts independently.
+- Publish source, commands, actual results, limitations, and AI-use notes for your self-review; never include credentials.