refactor: remove dead bind flow and rename MCP Tool to Gateway Target

[aidandaly24]

Description

Two cleanup changes for the gateway target wizard:

1. Remove dead bind flow — With feat: wire existing-endpoint flow for gateway targets #455 merged, the gateway target wizard goes directly to the existing-endpoint flow (name → endpoint → gateway → confirm). The mode selection ("Create new MCP
   tool" vs "Bind existing MCP runtime") and all bind flow screens were no longer reachable. Removes MODE_OPTIONS, all bind-related flow states, bind-specific hooks, and sets initial flow state
   to create-wizard.

2. Rename "MCP Tool" → "Gateway Target" — Updates all user-facing UI labels, CLI output messages, error messages, and code comments across 23 files. The internal code rename was done in refactor: rename mcp tool to gateway target #377
   but the UI strings were left as "MCP Tool". This completes the terminology migration.

Changes:

• Remove mode selection screen and bind flow from AddGatewayTargetFlow.tsx (8 additions, 199 deletions)
• Rename "MCP Tool" / "MCP tool" to "Gateway Target" / "gateway target" in TUI screens, CLI commands, operations, templates, schema, and tests (42 replacements across 23 files)
• Update CDK asset snapshot for cdk/bin/cdk.ts

Related Issue

Bug 1 and Bug 2 from Phase 1 Gateway tester feedback.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe): Dead code removal + terminology fix

Testing

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[notgitika]

LGTM!

[notgitika]

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