ADFA-5270 | Adopt shared secret store, fix terminal-tool dedup, and cover MCP flows

[jatezzz]

Description

This PR addresses duplicated cryptography logic, fixes an agent loop bug, and improves test coverage:

• Cryptography Centralization: Delegates AES/GCM encryption for ai-agent-mcp, ai-agent-gemini, and ai-agent-openai to the host's KeystoreSecretStore. The duplicate AndroidKeyStore references have been removed, and plugin.min_ide_version is bumped to 26.35. Each plugin retains its existing distinct alias so previously stored credentials migrate seamlessly.
• Tool Deduplication: Replaces the hardcoded it.name == RESPOND_TOOL check in ChatViewModel with the isTerminalToolName helper, ensuring backend variations like "Respond" are properly filtered out and the duplicate-turn check matches correctly.
• MCP Coverage & KDoc: Adds JVM test coverage for MCP session keep-alive across calls (McpSessionLifecycleTest), McpServerStore preferences lock, and McpPlugin scope cancellation. Corrects the McpServerStore.hasHeaders KDoc to accurately reflect its boolean return type.

Details

• All AI plugins build successfully against the refreshed libs/.
• JVM test suites pass, providing safe, host-independent validation of MCP connection logic and thread-safe preference locks.

Screen_Recording_20260825_162828_Code.on.the.Go.mp4

Ticket

ADFA-5270
Parent: ADFA-5255

Observation

By eliminating the redundant AES/GCM implementations, we prevent further code drift between the three AI plugins. The deduplication fix will prevent agents from getting stuck in terminal tool loops.

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