fix: add scaffolding triggers and reference loading guide to supabase-postgres-best-practices

[JesseVent]

Problem

supabase-postgres-best-practices references never load when an agent is given a greenfield scaffolding task. Prompts like create a supabase backend, use supabase as the database, or I'm building a new app with Supabase previously returned zero references from this skill — the agent proceeded using stale training data to make schema decisions.

Tested against claude-haiku-4.5 without the skill, the model produced @supabase/auth-helpers-nextjs (deprecated), NEXT_PUBLIC_SUPABASE_ANON_KEY (old key name), and createClient as a singleton (wrong pattern for App Router).

Root Cause

Two compounding issues:

1. Description only triggers on optimization vocabulary

An agent scaffolding a new project isn't "optimizing" — it's building from scratch. The trigger never fires.

2. Skill body had no conditional loading guidance

The model was left guessing which references to load from file titles alone. For vague prompts, titles like query-missing-indexes.md don't match.

Changes

• Description — added scaffolding/setup trigger phrases
• Reference Loading Guide — new table mapping scenarios to the references that should load first, modelled on the conditional loading pattern in the base supabase skill

Eval Results

Tested with claude-haiku-4.5, 97 prompts.

Prompt	Before	After
create a supabase backend	0 references	schema-primary-keys, schema-data-types, security-rls-basics + more
use supabase as the database	0 references	schema-primary-keys, schema-data-types, security-rls-basics
I'm building a new app with Supabase	0 references	schema-primary-keys, schema-data-types, security-rls-basics
I'm new to Supabase, where do I start	0 references	schema-primary-keys, schema-data-types, security-rls-basics

Total reference loads across all 97 prompts: 227 → 245 (+18). No regressions on existing prompts. All 63 tests pass.

Closes #100