fix: display aliased tool names in UI (#2564)

[clouatre]

Fixes #2564

Problem

The toolAliases feature works functionally (tools execute correctly), but the UI displays original tool names instead of the configured aliases.

Before:

🛠️  Using tool: getConfluencePage from mcp server atlassian_slalom

After:

🛠️  Using tool: getSlalomPage from mcp server atlassian_slalom

Solution

Added a display_name field to CustomTool to separate display concerns from MCP invocation:

• name field: Original tool name (sent to MCP server)
• display_name field: Aliased name (shown in UI)
• display_name() method: Uses alias if present, falls back to original name

Testing

• ✅ All existing tests pass (327 passed, 0 failed)
• ✅ Clippy clean (no new warnings)
• ✅ Code formatted with cargo +nightly fmt
• ✅ Manually tested with multi-instance MCP agent
• ✅ Verified: UI shows alias, MCP receives original name, tools execute correctly

Changes

• crates/chat-cli/src/cli/chat/tools/custom_tool.rs: Add display_name field
• crates/chat-cli/src/cli/chat/tools/mod.rs: Update display_name() to use alias
• crates/chat-cli/src/cli/chat/tool_manager.rs: Set display_name when creating CustomTool

Impact: Cosmetic fix only, fully backward compatible (Optional field with fallback)

[clouatre]

This PR completes the toolAliases implementation to match the documented behavior in agent-format.md.

Before this change, the UI displayed original tool names while the model used aliases, creating a confusing mismatch. This fix ensures all three layers are consistent:

• Model: Sees aliased names
• MCP invocation: Uses original names
• UI display: Shows aliased names

The display_name field separates display concerns from MCP protocol requirements, completing the documented specification.