fix(test): use valid URI format for plan handle IDs

- Update plan handle ID format to match TimeSafari specification
  - Default format: https://endorser.ch/entity/{26-char-ULID}
  - ULID: 26 characters, Crockford base32 encoded
  - Validates RFC 3986 URI format

- Add ULID generation functions
  - generateULID() creates 26-character Crockford base32 strings
  - generateValidPlanHandleId() creates full URI format IDs
  - Auto-generates valid IDs for testing

- Update DEFAULT_TEST_PROJECT_IDS
  - Now generates valid URI format IDs automatically
  - Removes placeholder warnings (IDs are now valid format)

- Add URI validation to seed scripts
  - Validates plan IDs match RFC 3986 URI format
  - Error messages with format examples
  - Blocks seeding with invalid formats

- Update test-user-zero.ts config
  - Auto-generates valid URI format plan IDs
  - Clear documentation of required format
  - Note that real IDs from database should replace test IDs

- Update documentation
  - Document default URI format specification
  - Explain ULID structure and encoding
  - Show examples of valid formats

This ensures all test project IDs match the actual TimeSafari plan
handle ID format, preventing validation errors during prefetch testing.

docs/getting-valid-plan-ids.md

@@ -62,14 +62,31 @@ cd /home/matthew/projects/timesafari/crowd-master
 
 ## Plan Handle ID Format
 
-Plan handle IDs can have different formats depending on your TimeSafari backend:
+Plan handle IDs **must be valid URIs** (RFC 3986 format).
 
-- **UUID format**: `550e8400-e29b-41d4-a716-446655440000`
-- **Hash format**: `abc123def456789`
-- **Sequential**: `plan_001`, `plan_002`
-- **Custom format**: Whatever your backend generates
+### Default Format (System-Generated)
 
-**Important**: Check your actual TimeSafari API/database to determine the correct format.
+**`https://endorser.ch/entity/{ULID}`**
+
+- **ULID**: 26-character string, Crockford base32 encoded
+- **Example**: `https://endorser.ch/entity/01GQBE7Q0RQQAGJMEEW6RSGKTF`
+
+### Custom Global URIs
+
+Any valid URI with a scheme is accepted:
+- `https://endorser.ch/entity/01GQBE7Q0RQQAGJMEEW6RSGKTF` (default)
+- `http://example.com/project/123` (custom)
+- `did:ethr:0x1234...` (DID format)
+- Any URI matching: `^[A-Za-z][A-Za-z0-9+.-]+:`
+
+**Validation**: The format must match RFC 3986 URI specification.
+
+### ULID Format Details
+
+- **Length**: Exactly 26 characters
+- **Encoding**: Crockford base32 (0-9, A-Z excluding I, L, O, U)
+- **Structure**: Timestamp + random component
+- **Purpose**: Globally unique, lexicographically sortable identifiers
 
 ## Updating Test Configuration