feat(dbml): @postgres/@sqlite dialect directives (#19)

Add parseable `@<namespace>[(<target>)]: <args>` directives embedded in DBML.
They are stored losslessly on each object's Metadata, round-trip unchanged
through the DBML writer, and are translated to SQL only by the writer for the
matching dialect.

- models: Directive type + catalog; Metadata map added to Column and Index
- dbml reader: parse and attach directives at database/table/column/index
  level; line-numbered errors; repeatable by default with singleton duplicate
  detection. Fixes a preexisting bug where an `indexes {}` closing brace ended
  the table early, dropping trailing Note: and directive lines.
- dbml writer: re-emit directives at their location; idempotent output
- pgsql writer: PARTITION BY / INHERITS / WITH / TABLESPACE (table),
  STORAGE / COMPRESSION / identity (column), WITH / TABLESPACE (index)
- sqlite writer: WITHOUT ROWID / STRICT (table), COLLATE (column)
- --strict-directives flag on ReaderOptions and WriterOptions
- docs/DBML_DIRECTIVES.md + reader/writer READMEs

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ss2MY5J11cRGwEz86ZXk7d

pkg/writers/sqlite/README.md

@@ -118,6 +118,21 @@ CREATE TABLE "posts" (
 - **Check Constraints**: Generated as comments (should be added to CREATE TABLE manually)
 - **Indexes**: Generated without PostgreSQL-specific features (no GIN, GiST, operator classes)
 
+## DBML dialect directives
+
+`@sqlite:` directives carried on a model object's `Metadata` (typically from a
+DBML source file) are translated to SQL:
+
+| Directive | Location | Emitted |
+|-----------|----------|---------|
+| `@sqlite: without rowid` | table | `WITHOUT ROWID` table option |
+| `@sqlite: strict` | table | `STRICT` table option (after `WITHOUT ROWID`) |
+| `@sqlite(col): collate …` | column | ` COLLATE …` in the column definition |
+
+Directives for other dialects (`@postgres:` …) are ignored. With
+`WriterOptions.StrictDirectives` (CLI `--strict-directives`) an untranslatable
+`@sqlite:` key is an error. Full reference: [`docs/DBML_DIRECTIVES.md`](../../../docs/DBML_DIRECTIVES.md).
+
 ## Output Structure
 
 Generated SQL follows this order: