Merge pull request #48 from pthm/custom-schema-fixes

Fix custom Postgres schema support and contextual tuples

Add v0.8.0 release notes blog post

Covers the three headline features since v0.7.4: modular model support
(fga.mod / Schema 1.2), configurable database schema, and safe identifier
truncation for PostgreSQL's 63-byte name limit.

Also documents the init wizard migration strategy selection, documentation
site refresh, and the breaking change to specialized function names (shorter
suffixes like _nw, _sub, _obj replacing _no_wildcard, _subjects, _objects).

Add v0.7.4 release notes blog post

Covers the two main features landing in v0.7.4:

- `melange generate migration` command for external migration framework
  integration (golang-migrate, sqlx, Flyway), with three comparison modes
  (database, git ref, previous schema file) and function-level change
  detection via SHA-256 checksums
- Two-phase skip detection in the built-in migrator to avoid unnecessary
  function re-application on version upgrades

Also documents config simplification, new unit/integration tests, gRPC
upgrade, documentation fixes, and migration notes for upgrading from v0.7.3.