feat: ui interface to interact with agentcore runtime agents

[massi-ang]

Description

Introduces a modern web interface for interacting with AgentCore agents and inspecting memory resources.

Key Features:

• Interactive chat interface with markdown support
• Session management and memory inspection
• OAuth and IAM authentication support
• Local and remote agent connectivity
• Mock mode for testing the UI

Components:

• React 19 + TypeScript frontend with Tailwind CSS
• FastAPI backend serving REST API and static assets
• introduces --ui flag to agentcore launch
• adds agentcore ui CLI commands to launch the UI only connecting to a remote agent

Requirements: Agents must accept input as {"prompt": "message"} to work with the UI.

Screenshots:

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Unit tests pass locally
• Integration tests pass (if applicable)
• Test coverage remains above 80%
• Manual testing completed

Checklist

• My code follows the project's style guidelines (ruff/pre-commit)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Security Checklist

• No hardcoded secrets or credentials
• No new security warnings from bandit
• Dependencies are from trusted sources
• No sensitive data logged

Breaking Changes

List any breaking changes and migration instructions:

N/A

Additional Notes

Add any additional notes or context about the PR here.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 88.33333% with 49 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@165496e). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ck_agentcore_starter_toolkit/ui/run_mock_server.py	0.00%	23 Missing ⚠️
...drock_agentcore_starter_toolkit/ui/backend/main.py	90.28%	10 Missing and 7 partials ⚠️
...rter_toolkit/ui/backend/services/config_service.py	89.47%	3 Missing and 3 partials ⚠️
...rter_toolkit/ui/backend/services/memory_service.py	96.96%	1 Missing and 1 partial ⚠️
..._agentcore_starter_toolkit/ui/backend/mock_mode.py	96.15%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #348   +/-   ##
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  Coverage        ?   86.58%           
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  Files           ?      126           
  Lines           ?    11054           
  Branches        ?     1664           
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  Hits            ?     9571           
  Misses          ?     1074           
  Partials        ?      409           

Flag	Coverage Δ
unittests	86.58% <88.33%> (?)

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[massi-ang]

Can someone review this PR?