Add recognition context support for Qwen3-ASR

[yukukotani]

Adds a shared recognition-context option across the public API, CLI, and language bindings, with Qwen3-ASR as the only model family that currently advertises and consumes it.

Why

Qwen3-ASR can use background text such as names, jargon, and domain terminology to improve recognition, but transcribe.cpp did not expose a way to provide that context. Reusing Whisper's initial_prompt would conflate two model-specific semantics and would not provide a consistent option across single, batch, and streaming APIs.

What

Core API and Qwen3-ASR

• Append context to transcribe_run_params and add the independent TRANSCRIBE_FEATURE_CONTEXT capability while preserving size-aware ABI compatibility.
• Copy streaming context into session-owned storage and warn, ignore, and continue when a model does not support recognition context.
• Insert Qwen3-ASR context into the system turn for single and batch decoding without normalization or truncation; context tokens count toward the decoder window.

CLI and bindings

• Add --context TEXT to the CLI.
• Expose recognition context through Python, TypeScript/JavaScript, Rust, Swift, and the Objective-C-compatible C module.
• Regenerate FFI layouts and update ABI hashes.

Tests and documentation

• Cover defaults, legacy struct prefixes, forwarding, unsupported-model behavior, streaming lifetime, prompt-token parity, input limits, CLI paths, and binding surfaces.
• Document recognition-context semantics and Qwen3-ASR input-limit behavior.

Notes

• Recognition context is intentionally separate from Whisper's initialPrompt / initial_prompt. Whisper's option is a Whisper-specific decoder prompt: it conditions decoding as transcript text preceding the current audio and can carry vocabulary, capitalization, punctuation, or style into the output. Qwen3-ASR recognition context is background information placed in the chat template's system turn to bias recognition toward names, jargon, and domain terminology. It is not prior transcript text, and it does not promise instruction following, translation, output formatting, punctuation, or style control.
• context is implemented in the common transcribe_run_params API rather than as a Qwen3-ASR-specific extension. This follows the earlier review discussion on PR #83, which noted that multiple model families have analogous recognition-context capabilities and that the option therefore belongs in the main API. Qwen3-ASR is currently the only family that advertises and consumes the capability; unsupported families warn and ignore it.