feat(presets): postgres-pgvector preset + dynamic DB picker

[geodro]

Adds the postgres-pgvector preset (v18 canonical, plus v17 and v16 alternates) so users wanting vector embeddings can install it as a first-class lerd service instead of hand-rolling a custom yaml. The image is pgvector/pgvector:pg, no PostGIS, host ports 5518/5517/5516 to avoid colliding with the default postgres preset.

While wiring it up, three rough edges around the postgres-family code paths needed fixing for pgvector to behave like every other DB family alternate. First, config.InferFamily only matches the - shape, so postgres-pgvector returned an empty family and cli/env.go decided it was not a database, skipping DB_DATABASE rewrite and createDatabase. Second, the env wizard and the MCP db_set tool hardcoded a sqlite/mysql/postgres choice, so pgvector was invisible to the pick UX even once installed. Third, the multi-version preset picker filtered the canonical version out, so users staring at the postgres-pgvector row saw only v17 and v16 in the dropdown with no obvious way to install v18.

Family resolution is now a single helper. config.FamilyOf(*CustomService) and config.FamilyOfName(string) prefer the explicit Family field over name-pattern inference, and the four sites that used to inline the same Family-then-InferFamily dance (serviceops/migrate.go, serviceops/serviceops.go, cli/init.go, plus the new env-side check) now route through it. config.IsDBServiceName is the same idea for the boolean "does this name refer to a DB" used by db_set validation and ReplaceProjectDBService.

The env wizard and db_set both build their option list dynamically from ServicesInFamily("mysql") + ServicesInFamily("postgres") + sqlite, so any installed family alternate (mariadb, mysql-5-7, postgres-pgvector, future ones) shows up by name. Picking pgvector in .lerd.yaml now correctly suppresses the default postgres preset via userPickedDBFromYAML and lands the right env_vars and DB creation in pgvector's container.

The preset picker dropdown gains canonical versions, marked (default) in the label and preselected via default_version. A new config.PresetVersionServiceName helper centralises the canonical-vs-suffixed name resolution so the CLI table, web UI handler, and MCP list all check install state through the same path. An installed canonical now correctly shows up in installed_tags and disappears from the dropdown the same way installed alternates always did, leaving only what the user can still install.

lerd-postgres-pgvector (and its alternates) participate in pgadmin auto-discovery via discover_family:postgres without any pgadmin-side change. There is no env_detect on the preset on purpose: DB_CONNECTION=pgsql already belongs to the default postgres detector, so first-clone auto-detection would require a tiebreaker we have not designed. The intended UX is install once via lerd service preset postgres-pgvector, pick once via wizard or db_set or .lerd.yaml, every subsequent lerd env re-run routes everything through pgvector.

Refs #378.