Plan: writers/template (8.5%)

Existing

Pure helper functions; one test file per source file, table-driven. Then render tests through the writer.

File	Funcs	Cases
`filters.go`	FilterTables, FilterTablesByPattern, FilterColumns, FilterColumnsByType, FilterPrimaryKeys, FilterForeignKeys, FilterUniqueConstraints, FilterCheckConstraints, FilterNullable, FilterNotNull, matchPattern	Empty input, no match, glob patterns, nil maps
`formatters.go`	ToJSON, ToJSONPretty, ToYAML, Indent, IndentWith, Escape, EscapeQuotes, Comment, QuoteString, UnquoteString	Empty string, multiline, special chars, marshal failure
`loop_helpers.go`	Enumerate, Batch, Chunk, Reverse, First, Last, Skip, Take, Concat, Unique, SortBy, GroupBy, CountIf, getFieldValue, compareValues	Empty, n > len, n <= 0, non-slice input, missing field
`safe_access.go`	Get, GetOr, GetPath, GetPathOr, SafeIndex, SafeIndexOr, Has, HasPath, Keys, Merge, Pick, Omit, SliceContains, IndexOf, Pluck	nil, missing key, nested path, out-of-range
`string_helpers.go`	ToUpper, ToLower, ToCamelCase, and rest	Empty, snake/kebab/space input, unicode
`errors.go`	Error, Unwrap, NewTemplate{Load,Parse,Execute}Error	errors.Is/As, message contents
`funcmap.go`	BuildFuncMap	Every registered name resolves and is callable
`type_mappers.go`, `template_data.go`	check after above
`writer.go`	WriteDatabase/Schema/Table, modes	Template load/parse/execute error paths; per-table, per-schema, whole-db modes; output to file vs stdout

2-3 small template fixtures in pkg/writers/template/testdata/ (valid, parse error, execute error).
Schema input: reuse tests/assets/dbml/simple.dbml / complex.dbml.