chore(ci): upgrade supabase CLI version pin

[chiptus]

Context

The deploy workflow currently pins supabase/setup-cli@v1 to version 2.58.5 (matching package.json). Worth a separate PR to bump to the latest stable and review the changelog.

Discovered during PR #32:

• The action's "auto-detect from package.json" feature is unreliable — it resolved to v2.20.3 despite package.json declaring ^2.58.5. Keep the version pinned explicitly when bumping.

As of CI run on 2026-05-16, latest was v2.98.2 (the CLI itself printed: A new version of Supabase CLI is available: v2.98.2 (currently installed v2.20.3)).

Scope

• Bump supabase in package.json (^2.58.5 → latest)
• Bump pinned version in .github/workflows/_db_migrate.yml
• Bump pinned version in .github/workflows/_deploy_edge_functions.yml
• Skim the changelog between 2.58 and target for breaking changes around db push, functions deploy, link, and migration repair
• Test by running the deploy workflow against staging via workflow_dispatch once merged to main

Why a separate PR

Isolates blast radius. If a CLI behavior change breaks db push or functions deploy, we want it in its own revertable commit, not mixed in with the workflow refactor in #32.