Summary

Adds focused attached Issue Field support to singular update_project_item name-form writes. This PR is stacked on #2903.

Why

Completes the singular Issue Field update path while preserving existing Project field behavior.

Addresses github/planning-tracking#3523

What changed

• Adds regression coverage showing existing field_names reads surface attached Issue Field values without changing read queries.
• Supports TEXT, NUMBER, DATE, and case-insensitive SINGLE_SELECT option-name writes, plus clears, through singular update_project_item by field name.
• Returns structured validation and unsupported item-type errors, and shares a conflict-free Issue Field mutation response.

MCP impact

• No tool or API changes
• Tool schema or behavior changed - singular name-form Project item updates now support attached Issue Fields.
• New tool added

Prompts tested (tool changes only)

• "Set the Customer field to Acme on this project issue."
• "Set Unicorn Type to Pegasus on this project issue."
• "Clear the Due Date field on this project issue."

Security / limits

• No security or limits impact - reuses existing Project and Issue Field permissions.
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)