Port Jimmy as @corbits/jimmy-agent

[TheGreatAxios]

Ports Jimmy from the scout repo into workbench as a self-contained agent package: @corbits/jimmy-agent carries the system prompt, the tool declaration, and the Giphy search tool body — the portable half of the agent, per corbitsdev/examples' defineAgent/createAgent split.

Ported vs. deferred

• Ported: the Giphy search HTTP client + response parsing (gif-search-tool.ts, from scout/packages/jimmy/src/giphy-search.ts), and the system prompt/agent shape (agent.ts, from index.ts's jimmyPackage), trimmed to one tool call and one reply.
• Deferred to v0.2 (owner's call): Slack dispatch, block-kit rendering, the /gif//jimmy Slack slash commands, and the 4-up picker + shuffle/cancel signal machine (scout/workflows/jimmy) — built for Slack's interactive buttons, no workbench-chat equivalent exists yet.
• Credential: binds host-side through the same CredentialCapability.resolve("giphy") seam every tool package in this repo uses (see @corbits/web-search-tools) — never a bare env var, never hardcoded. A missing/unbound credential returns a "connect Giphy" isError result, never a silent empty reply or a thrown error.

What is NOT yet wired (correction to this PR's earlier description)

Two integration steps remain before @Jimmy//jimmy actually resolves in workbench chat — this package alone does not make that happen:

1. No giphy connector exists yet. packages/connections/src/registry.ts's CONNECTOR_REGISTRY has no giphy entry, and none of the three existing credential-provider plugins (http, http-raw-authorization, http-x-api-key) put the secret on the query string the way Giphy's /v1/gifs/search endpoint requires — a fourth plugin (mirroring http-x-api-key-provider.ts, query param instead of header) is the missing piece. Until it lands, gif_search always returns the connect prompt.
2. No workflow wrapper or deployment. packages/chat's listInvitableDefinitions (platform-adapter.ts) only returns workflowDefinition rows with status: "deployed" for a tenant — that's what makes a name resolvable as @name//name (@corbits/commands' createWorkflowCommandPlugin derives one command per invitable definition automatically). This PR ships the AgentDefinition only; it does not add a wf_jimmy workflow wrapper (the shape @corbits/code-review-workflow uses over @corbits/code-review's definition) or deploy one to any tenant. Both are needed before @Jimmy resolves to anything in chat.

Verification

bun test in packages/jimmy-agent — 6 pass: a stubbed Giphy response returns a GIF CDN URL; an unbound/absent credential returns the "connect Giphy" error rather than throwing or replying empty. bun run typecheck in-package passes. Repo-root check:packages, check:licenses, check:tool-package-pins all pass. Repo-root bun run check / lint were not run locally (dev-machine memory pressure running many concurrent worktree checks) — left to CI on this PR.