Add tests for build_claude_command with permission/sandbox flags

[geoffjay]

Context

Child of #78. Depends on #116, #117.

Changes

Add unit tests covering:

build_claude_command tests

• Permission mode flag output for each PermissionMode variant
• Single and multiple allowed_tools flags
• Single and multiple disallowed_tools flags
• Tools flag with comma-separated values
• skip_permissions flag
• Combinations: permission_mode + tools + skip_permissions
• No flags emitted when all fields are at defaults
• Interactive mode: verify no permission flags emitted (they're Claude CLI flags for SDK mode)

PermissionMode serialization tests

• Round-trip serialization/deserialization for each variant
• JSON format matches camelCase (e.g., "acceptEdits", "bypassPermissions")

AgentConfig serde tests

• Deserialize config with new fields present
• Deserialize config with new fields absent (backward compatibility)

Files

• crates/orchestrator/src/manager.rs or new test module
• crates/orchestrator/src/types.rs — test module

Acceptance Criteria

• Full coverage of build_claude_command() flag combinations
• PermissionMode serde round-trip tests
• Backward-compatible deserialization test
• All tests pass with cargo test -p agentd-orchestrator