Declaration-build failures surface as catch-all AB5000 with the TypeScript diagnostics swallowed

[ScriptedAlchemy]

Problem

Today an emit-only TS4023 regression—exported factories referencing an unexported type (#150 / #174)—surfaced only as:

error Failed to generate declaration files. (agent-bundle-index)
[{"code":"AB5000","message":"Error occurred in agent-bundle-index declaration files generation."}]

The five underlying TS4023 diagnostics were hidden by rslib's one-line error.

This creates two DX problems:

1. It conflates declaration-build failures with AB5000's dev-lock meaning ("another dev process owns this project"), which misled initial triage.
2. It forced a manual tsc --declaration --emitDeclarationOnly replay to reveal the actual errors.

Requested improvements

• Surface the underlying TypeScript diagnostics—including file, line, and diagnostic code—through the declaration-build failure path.
• Give declaration-build failures their own AB code instead of using the AB5000 catch-all.
• Add a hint that emit-only errors can be invisible to --noEmit.

See #174's root-cause writeup for the concrete regression and diagnosis.

[ScriptedAlchemy]

Delivered in #265 (merge cee25b8).

• Declaration-build failures now report the dedicated AB4716 code (AB471x package-build lib family) — never the AB5000 catch-all whose dev-lock meaning misled the feat(routes): migrate audiobook curator to public authoring #150/fix(examples): export CliCommandDefinition so declaration emit can name it #174 triage.
• The underlying TypeScript diagnostics are surfaced: when the dts pass aborts, the build replays declaration emit over the same synthesized tsconfig with the consumer project's own typescript, and emits one AB4716 error per recovered diagnostic with file, (line,column), TS code, and compiler message (plus sourcePath), in both human and --json output.
• Every AB4716 carries the requested hint: emit-only errors such as TS4023 never appear under tsc --noEmit; reproduce with tsc --declaration --emitDeclarationOnly.
• If nothing can be recovered (no resolvable typescript, or the replay passes), the failure still reports as a single AB4716 with the bundler's message.
• Documented in docs/diagnostics.md; covered by an integration test reproducing the feat(routes): migrate audiobook curator to public authoring #150-shape TS4023 fixture end-to-end through the CLI.

Known limitation (noted in the PR): detection keys on rsbuild-plugin-dts's prose failure line since it exposes no structured signal; a reworded upstream message degrades to the old catch-all rather than breaking.