fix: surface error instead of panicking on unclosed exported namespace/module

[ammubhave]

Summary

Fixes #802.

Formatting a file with an unclosed exported namespace/module panicked with Expected to find a close brace token. instead of reporting a syntax error:

export namespace Foo {
  const x = 1;

Root cause

swc's parser recovers from the missing } for the export namespace/export module case and produces a TsModuleDecl without emitting any diagnostic (verified: 0 diagnostics). The parse-time gate ensure_no_specific_syntax_errors therefore has nothing to filter, so code generation proceeds and gen_membered_body panics on .expect("Expected to find a close brace token.").

Every other unclosed form (bare namespace, declare namespace/module/global, bare module, dotted namespace Foo.Bar) does emit an swc diagnostic and was already handled.

Fix

When no close-brace token is found in gen_membered_body, push a generation diagnostic (which makes generate return an Err) instead of .expect()-panicking. This reuses the existing context.diagnostics error channel and, because it relies on the view's direct-token-ownership, also handles nested cases where the single } belongs to the inner block.

The resulting error is, e.g.:

Unexpected end of file. Expected a close brace token for the block starting on line 1.

Tests

Added unit tests in src/format_text.rs covering the panic→error variants (simple, export module, empty body, nested, unclosed-outer-with-complete-inner, dotted name) — including exact-message assertions that pin the reported line — plus regression cases confirming well-formed namespaces still format.

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