fix(llms): parse Titan results outputText

[aniruddhaadak80]

Linked Issue

Closes #7336

Description

Legacy amazon (Titan) invoke_model responses always parsed to "", causing silent memory loss in Memory.add(). The request builder sends Titan shape (inputText / textGenerationConfig) but _parse_response read top-level completion, which Titan never returns (AWS shape is results[0].outputText). This PR reads results[0].outputText first and keeps completion as fallback for compat; empty/missing still returns "". Nova path untouched.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactor (no functional changes)
• Documentation update

AI Assistance

• No AI assistance

• AI-assisted (autocomplete, or I asked a model questions while writing this)

• AI-generated (an agent wrote most or all of this diff)

• I can explain every line of this diff and how it interacts with the rest of the codebase, without asking an AI tool.

Tool: Muse Spark (OpenCode). I verified the repro before/after, ran targeted pytest, and ran ruff check locally.

Breaking Changes

N/A

Test Coverage

• I added/updated unit tests
• I added/updated integration tests
• I tested manually (describe below)
• No tests needed (explain why)

Titan body → "Hi from Titan" (test_titan_results_output_text, test_titan_generate_response); Nova content[0].text unchanged (test_nova_content_unchanged); missing/empty → ""; legacy completion fallback kept. pytest tests/llms/test_aws_bedrock.py -v: 58 passed. ruff check clean. New tests fail without fix ('' vs 'Hi from Titan').

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have added tests that prove my fix/feature works
• New and existing tests pass locally
• I have updated documentation if needed

[github-actions]

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[CLAassistant]

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[github-actions]

Hi @aniruddhaadak80, thanks for opening this pull request.

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