docs: PostGIS discovery & connect API endpoints (5 routes) completely missing from behaviors.md

[evan-zhang11]

Problem

The PostGIS registration workflow includes 5 API endpoints that are completely undocumented in docs/dev/behaviors.md:

Undocumented Endpoints

#	Endpoint	Method	Purpose
1	/api/postgis/connections/discover-schemas	POST	List all user schemas in a PostGIS database
2	/api/postgis/connections/discover-tables	POST	List tables/views in a specific schema
3	/api/postgis/connections/discover-columns	POST	List geometry columns and FID candidates for a table
4	/api/postgis/connections/discover-objects	POST	List ALL spatial objects across all user schemas
5	/api/postgis/connections/connect	POST	Combined: test connection + discover spatial objects + check existing sources

Implementation Details

All 5 endpoints are defined in backend/src/postgis.rs and registered in backend/src/routes.rs.

Common characteristics:

• All require authentication and admin role (require_postgis_admin)
• Accept PostgisConnectionConfig in the request body (host, port, database, username, password, sslMode)
• sslMode=disable is the only supported value (MVP constraint)

Endpoint-specific responses:

1. discover-schemas → { schemas: [String] }
2. discover-tables → { tables: [{ name, table_type }] } (requires schema param)
3. discover-columns → { geometry_columns: [{ column_name, srid, geometry_type }], fid_candidates: [String] } (requires schema + table params)
4. discover-objects → { objects: [{ schema, table, table_type, geometry_columns, existing_file_id, row_count }] }
5. connect → { success, server_version, postgis_version, objects: [...] } — similar to discover-objects but also returns version info and checks if objects are already registered as sources in the current workspace

Relationship Between Endpoints

The discover-* endpoints provide a granular, wizard-style registration flow:

1. connect or discover-objects → get overview of all available spatial data
2. discover-schemas → pick a schema
3. discover-tables → pick a table/view within that schema
4. discover-columns → select geometry column and FID column
5. Finally, register (API-019) creates the data source

The connect endpoint appears to be a legacy/combined endpoint that overlaps with discover-objects but adds version info and existing-source lookup.

Current Documentation

Only these PostGIS endpoints are documented:

• API-018: POST /api/postgis/connections/test (connection test only)
• API-019: POST /api/postgis/sources/register (register a source)

The discovery workflow between test and register is completely undocumented.

Proposed Action

Add behavior contract entries (API-020a through API-020e, or a new module section) for the 5 discovery/connect endpoints. Each should document:

• Request body schema
• Response body schema
• Error responses (400 for connection failure, 401 for unauthenticated, 403 for non-admin)
• Expected status codes

Priority: P1 — These endpoints power the PostGIS registration wizard UI and should be documented as they represent significant user-facing functionality.