FN-5652: add goal retrieval tool for agent execution

Expose goal details to agents during task execution workflows.

- add fn_goal_show tool to the CLI extension with goal lookup, formatted output, and not-found error details
- add focused tests for goal tool registration and execution behavior
- mark fn_goal_show as execution-safe in engine gating classifications and test coverage
- update Fusion skill/reference docs to include the new goal retrieval capability
- add a changeset for @runfusion/fusion patch release

Files changed:
 .changeset/fn-5652-goal-show.md                    |   7 +
 packages/cli/skill/fusion/SKILL.md                 |   2 +-
 .../cli/skill/fusion/references/extension-tools.md |  16 +++
 .../skill/fusion/references/fusion-capabilities.md |   1 +
 .../cli/src/__tests__/extension-goal-tools.test.ts | 148 +++++++++++++++++++++
 packages/cli/src/extension.ts                      |  43 ++++++
 .../src/__tests__/gating-classifications.test.ts   |   7 +
 packages/engine/src/gating-classifications.ts      |   2 +
 8 files changed, 225 insertions(+), 1 deletion(-)

Fusion-Task-Id: FN-5652

Fusion-Task-Lineage: 98c2c417-0887-4794-81b1-6b47ab0f708f

packages/engine/src/gating-classifications.ts

@@ -89,6 +89,8 @@ export const READONLY_FN_TOOLS: ReadonlySet<string> = new Set([
   "fn_insight_show",
   "fn_insight_run_list",
   "fn_insight_run_show",
+  "fn_goal_list",
+  "fn_goal_show",
   "fn_mission_list",
   "fn_mission_show",
   "fn_list_agents",