chore: scaffold from seamless-templates v0.5.0

[Bccorb]

Bumps SEAMLESS_TEMPLATES_REF from v0.4.0 to v0.5.0, the release that carries the express
starter's DATABASE_URL and TLS support (fells-code/seamless-templates#22).

This is the step that makes #141 take effect. The CLI already computed the managed connection string,
but applyTemplateEnv only writes keys the manifest declares, and v0.4.0 did not declare
{{databaseUrl}}, so nothing was written.

Verified against the published tag

Not a fixture: I ran the real openTemplateSource at v0.5.0, copied the express starter into temp
directories, and applied applyTemplateEnv with both scaffold contexts.

• The manifest declares DATABASE_URL: {{databaseUrl}}.
• A managed context writes
  DATABASE_URL=postgres://USER:PASSWORD@db.example.com:5432/tenant?sslmode=require.
• A local context writes DATABASE_URL=, so the starter falls back to its discrete DB_* values, as
  the compose stack needs.
• src/lib/databaseUrl.ts is present in the copied template.

That empty-local case was the one that could have broken the existing flow: an unresolved placeholder
throws, so a missing databaseUrl on the local path would have failed every local scaffold.

npm run build and npm test pass (691 passed, 4 skipped), coverage unchanged at 99.37% lines.

Still open

cliMin in the templates manifest is still 0.10.0. Raising it needs another templates release and
buys little, since the CLI only ever fetches the ref it pins. Worth folding into the next templates
change rather than releasing for it alone.

The TLS certificate question stands: if a tenant's Postgres presents a certificate that does not chain
to a public CA, managed connections fail until DB_SSL_REJECT_UNAUTHORIZED=false is set. First live
trial will tell us, and if it does not chain we should ship the CA rather than flip the default.