V106: Split phoenix_kit_projects.name uniqueness across templates and real projects.

V101 created a single global unique index (phoenix_kit_projects_name_index) on lower(name) over the phoenix_kit_projects table. Templates and real projects share that table — distinguished only by the is_template boolean — so they also shared one name namespace, which made Projects.create_project_from_template/2 collide whenever a real project should reuse the source template's name (the common, expected case).

This migration replaces that single index with two partial unique indexes — one per is_template value — so a template "Onboarding" and a real project "Onboarding" can coexist freely.

Indexes

• phoenix_kit_projects_name_template_index UNIQUE (lower(name)) WHERE is_template = true
• phoenix_kit_projects_name_project_index UNIQUE (lower(name)) WHERE is_template = false

Both are idempotent (CREATE INDEX IF NOT EXISTS / DROP INDEX IF EXISTS).

Schema-side change only. The Ecto changeset's unique_constraint(:name, name: :phoenix_kit_projects_name_index, ...) reference is updated in the same release of phoenix_kit_projects to point at whichever partial index applies (the is_template value at validate time selects the correct constraint name).