Enhance validation and fix execom roster management

[DevWithPranav]

No description provided.

[greptile-apps]

Greptile Summary

This PR replaces the campus execom role blacklist with explicit role classification. The main changes are:

• Adds is_execom_role to the Role model.
• Marks newly created custom and IG campus-lead roles.
• Rejects execom titles already used by non-execom roles.
• Filters campus rosters by the new role flag.

Confidence Score: 4/5

The role schema and historical execom classification need fixes before merging.

• The current database schema lacks the column used by new reads and writes.
• Existing legitimate execom roles will remain false and disappear from campus rosters without a backfill.

db/user.py and api/dashboard/campus/events_views.py

Important Files Changed

Filename	Overview
db/user.py	Adds an unmanaged model field without the required database schema artifact.
api/dashboard/campus/events_views.py	Switches roster selection to explicit role classification without backfilling historical roles.
api/dashboard/campus/dash_campus_helper.py	Classifies newly created IG roles, but creation defaults do not update existing rows.
api/dashboard/ig/dash_ig_view.py	Adds classification values when creating new IG roles.

_{Reviews (1): Last reviewed commit: "Merge pull request #3061 from gtech-mule..." | Re-trigger Greptile}

[greptile-apps]

Unmanaged Column Is Missing

Role is unmanaged, but this PR does not add is_execom_role to schema.sql or an alter script. Deploying against the current schema makes the new role filters and writes fail with an unknown-column database error.

[greptile-apps]

Historical Execom Roles Disappear

Existing Campus Lead, Lead Enabler, Enabler, and IG campus-lead rows predate this flag and are not backfilled here. Once the column exists with its false default, this positive filter removes their current holders from GET /campus/execom/, whereas the previous blacklist included them.