feat(wizard): add Create button for JIRA cost custom field

[aaight]

Summary

• Adds ADD_JIRA_PROJECT_CUSTOM_FIELD action to WizardAction type and wizardReducer — appends { id, name, custom: true } to jiraProjectDetails.fields
• Adds useJiraCustomFieldCreation hook in pm-wizard-hooks.ts — calls createJiraCustomField tRPC mutation, dispatches ADD_JIRA_PROJECT_CUSTOM_FIELD + SET_JIRA_COST_FIELD on success, shows clear error about admin permissions on failure
• Adds Plus "Create" button next to the cost field label in JiraFieldMappingStep — visible only when project details are loaded and no cost field is selected
• Button shows Loader2 spinner during creation and is disabled while creating
• Adds admin permission note below the label explaining JIRA custom fields are global
• Wires handler and loading state through PMWizard orchestrator

Card: https://trello.com/c/jDPVbE8y/310-as-an-admin-i-want-a-create-button-next-to-the-jira-cost-field-dropdown-so-that-i-can-create-a-cost-custom-field-without-leaving

Test plan

• Navigate to PM wizard for a JIRA project
• Verify the "Create" button appears next to "Custom Field: Cost" when project details are loaded and no cost field is selected
• Click "Create" — button should show spinner and become disabled during creation
• On success, the new "Cost" field should appear in the dropdown and be auto-selected
• On failure (non-admin user), should see error message mentioning admin permissions
• All existing tests pass

🤖 Generated with Claude Code

[nhopeatall]

Summary

Clean, well-structured feature that mirrors the existing Trello custom field creation pattern. The reducer, hook, UI, and orchestrator wiring are all correct. One gap worth addressing: the JIRA Create button lacks the duplicate-field guard that the Trello equivalent has.

Should Fix

• web/src/components/projects/pm-wizard-jira-steps.tsx:277 — Missing duplicate-field guard. The Create button visibility condition only checks !state.jiraCostFieldId (no field selected), but unlike the Trello equivalent (lines 308-315 of pm-wizard-trello-steps.tsx), it does not check whether a "Cost" field already exists in state.jiraProjectDetails.fields. If a "Cost" field already exists but isn't selected yet, the button still appears, and clicking it creates a duplicate global custom field in JIRA.

  The Trello equivalent does this:

  const existingCostField = state.trelloBoardDetails?.customFields.some(
    (f) => f.type === "number" && f.name.toLowerCase() === "cost",
  );
  const showCreateCostButton = state.trelloBoardDetails && onCreateCostField && !state.trelloCostFieldId && !existingCostField;

  The JIRA version should add a similar check, e.g.:

  const existingCostField = state.jiraProjectDetails.fields.some(
    (f) => f.name.toLowerCase() === "cost"
  );

  Since JIRA custom fields are global (as the PR's own info text correctly notes), creating duplicates is particularly problematic.

[nhopeatall]

Summary

LGTM — Clean, well-structured feature addition that follows the existing Trello custom field creation pattern exactly.

The implementation correctly:

• Adds reducer action ADD_JIRA_PROJECT_CUSTOM_FIELD matching the JiraProjectDetails.fields shape ({ id, name, custom })
• Creates useJiraCustomFieldCreation hook following the same mutation pattern as useTrelloCustomFieldCreation
• Spreads { ...field, custom: true } in onSuccess to augment the API response ({ id, name }) with the required custom boolean
• Hides the Create button when a cost field already exists in the project OR when one is already selected
• Calls the hook unconditionally in PMWizard (correct for Rules of Hooks)
• Wires loading state through the orchestrator matching the existing Trello pattern
• Backend endpoint + tests already exist — this PR only adds the frontend wiring

All CI checks pass.