PM-5800: Hide copilot fee for task challenges

[jmgasper]

What was broken

Task challenge setup in the Work app displayed a Copilot Fee field, allowing project managers to bundle a copilot payment with the task instead of recording the copilot work as a separate task payment.

Root cause

The challenge editor rendered the copilot fee input for every billable challenge without considering the resolved task challenge state.

What was changed

• Hide the copilot fee input and its layout column for task challenges.
• Keep copilot assignment and the rest of task billing unchanged.
• Preserve the copilot fee input for non-task challenges.
• Document that the fee input is available only for non-task challenges.

Any added/updated tests

• Added form coverage that verifies task challenges hide the fee while retaining copilot assignment and billing.
• Added coverage that verifies non-task challenges still show the fee.
• The two focused PM-5800 tests pass.
• Lint passes.
• The production build passes with existing warnings.
• The full test suite was run and matches the fetched origin/dev baseline: 18 suites and 32 tests fail both before and after this change. This branch adds two passing tests, increasing the passing total from 999 to 1001 without adding failures.