…_prompt, and session/clear

Add ACP custom method handlers to close the gaps identified in issue block#7225.
Routes CLI prompt listing, provider info, plan prompt, and session clear
through goosed via ACP custom methods.

New ACP methods:
- _goose/config/prompts: list extension prompts for a session
- _goose/config/prompt_info: get details for a single prompt by name
- _goose/agent/provider_info: get provider, model, context limit, tokens
- _goose/agent/plan_prompt: get the plan prompt string for a session
- _goose/session/clear: clear conversation and reset token counts

All new request types include #[serde(rename_all = "camelCase")] for
JSON field naming consistency with existing types.

Includes 7 integration tests covering all new methods and error cases,
using the existing AcpServerConnection, SessionData, and send_custom
test infrastructure.

Signed-off-by: fre <[email protected]>

Replace the single cancel_token + prompt_finished pair in GooseAcpSession
with a Vec<ActivePrompt>, where each in-flight prompt owns its own
CancellationToken and Notify.

This fixes two concurrency issues:

1. prompt_finished Notify was replaced each time a new prompt started in
   get_session_agent. If prompt B started before prompt A exited, A would
   notify B's Notify instead of its own, leaving session/clear blocked
   indefinitely on the original Notify.

2. cancel_token was overwritten by each new prompt, so session/clear only
   cancelled/waited for the latest prompt while older prompt tasks could
   continue streaming and append messages after clear returned.

Now on_cancel, on_close_session, and on_clear_session iterate all
active_prompts, cancelling every token and (for clear) awaiting every
finished signal.

Signed-off-by: fre <[email protected]>

…ptInfoResponse

Replace serde_json::Value with typed fields:
- ListPromptsResponse.prompts: HashMap<String, Vec<rmcp::model::Prompt>>
- GetPromptInfoResponse.prompt: rmcp::model::Prompt
Remove intermediate serde_json::to_value calls in server.rs handlers.

Signed-off-by: fre <[email protected]>

…ookup

P1: Add a 10s timeout to notify.notified().await in _goose/session/clear
so a stalled provider stream cannot block the clear indefinitely.

P2: Collect all matching prompts across extensions in prompt_info handler;
return an explicit ambiguity error when duplicate names exist instead of
non-deterministic HashMap iteration.

Signed-off-by: fre <[email protected]>

Replace sequential per-notify timeout loop with
futures::future::join_all wrapped in one tokio::time::timeout,
bounding total clear latency to 10s regardless of active prompt count.

Signed-off-by: fre <[email protected]>