Agent Ops and Telemetry

## Problem

The initial agent-context and provider-prompting work improved the runtime, but three follow-ons were still missing:

- admins had no first-class UI to author the durable `agent_context` business profile
- runtime prompt-caching and context-management behavior were invisible in cost views and tools
- prompt quality changes were not protected by focused regression fixtures

## Solution

### Workspace Context Authoring

Add a dedicated editor to **Admin > Agents** that reads and writes the typed `agent_context` tenant setting. This makes durable workspace business knowledge editable without modifying seeded agents or shipping a code change.

### Runtime Telemetry

Emit `ai.runtime.completed` analytics events from the shared agent runtime with:

- model and source
- cache read/write token totals
- reasoning token totals
- whether prompt caching was configured
- whether context management was configured
- how many context edits were actually applied

Aggregate those signals into the admin cost surface and the `getUsageStats` tool.

### Regression Coverage

Add fixture-backed prompt regression tests for:

- OCI workspace-business-context rendering
- the key operating-language expectations in seeded system-agent prompts

## Outcome

- Workspace business context is now editable in the admin UI.
- Cost dashboards and tools can show cache reuse, cache writes, reasoning usage, and context-management activity.
- Prompt regressions now fail fast in tests instead of drifting silently.