feat(mcp): improve project context awareness in MCP tool descriptions

[github-actions]

Problem

AI agents querying Hookdeck via MCP did not have enough signal in tool descriptions to know that all queries are scoped to an active project. When a user referenced a project by name, agents silently used whatever project was active, returning data from the wrong project with no warning.

Solution

Tool description updates (tools.go)

• hookdeck_projects: Replaced the passive description with imperative language making it the required first step when a user references a project by name. Clarifies that all queries are scoped to the active project.
• hookdeck_connections, hookdeck_events, hookdeck_issues, hookdeck_metrics, hookdeck_requests: Appended "Results are scoped to the active project — call hookdeck_projects first if the user has specified a project."
• hookdeck_help: Appended a note that all tools operate on the active project.

Help text updates (tool_help.go)

• Updated the help overview to show a prominent "All tools operate on the active project" notice.
• Added the same project-scoping note to each of the five query-tool detailed help entries.
• Expanded the hookdeck_projects help entry with the same imperative language.

Response envelope (response.go, query tool handlers)

Implemented the "Additional Consideration" from the issue: added a JSONResultWithProjectID helper that merges active_project_id into every list/metrics response. Updated list handlers in tool_events.go, tool_issues.go, tool_connections.go, tool_requests.go, and all four functions in tool_metrics.go to use this helper. This lets agents self-verify that results came from the intended project even after a query runs.