feat(gateway-target): expose toolOverrides and multiple toolFilters via CLI flags

[aidandaly24]

Description

AWS::BedrockAgentCore::GatewayTarget.TargetConfiguration.Mcp.ApiGateway.ApiGatewayToolConfiguration exposes two arrays customers use to control which tools are generated from an upstream API Gateway target:

• ToolFilters — array of ApiGatewayToolFilter (FilterPath + Methods) — restricts which routes become tools.
• ToolOverrides — array of ApiGatewayToolOverride — explicit tool definitions with custom names/descriptions/method/path overrides.

Source: ApiGatewayToolConfiguration CFN docs.

CLI status today (verified in this codebase):

• The schema in src/schema/schemas/mcp.ts:72–86 defines both ApiGatewayToolFilterSchema and ApiGatewayToolOverrideSchema.
• The L3 construct (@aws/agentcore-cdk — src/cdk/constructs/components/mcp/Gateway.ts:324–336) passes both through to CFN.
• agentcore add gateway-target exposes --tool-filter-path and --tool-filter-methods (single filter only; see src/cli/commands/add/types.ts:83–84 and validate.ts:503–506).
• There is no CLI flag for toolOverrides — customers can only set them by hand-editing agentcore.json or by importing from another project.
• The TUI does not surface either filters or overrides as a first-class step.

Acceptance Criteria

• Allow multiple --tool-filter-path / --tool-filter-methods pairs on a single command (today only one filter is accepted).
• Add CLI flags for toolOverrides — either repeatable --tool-override JSON args or a --tool-overrides-file <path> flag pointing to a JSON file.
• Surface tool filter and tool override entry in the AddGatewayTargetFlow.tsx TUI, gated behind an "Advanced API Gateway options" sub-screen.
• Document the difference (filters = subset, overrides = explicit) in CLI help text.
• Validate filters/overrides against the upstream API Gateway's known routes during agentcore deploy --diff if possible.
• Snapshot tests covering the new flags.

Additional Context

• CFN support: YES — both ToolFilters and ToolOverrides are in CFN.
• L3 surface: already complete — this issue is purely CLI/TUI.
• Existing import path covers them (src/cli/commands/import/import-gateway.ts:76–82); reuse the mapping helper for the new add flow.
• Existing single-filter flag pair: --tool-filter-path, --tool-filter-methods — needs to become repeatable.