Insights: session tagging for grouping dispatch agents into initiatives

Problem

When using /insights, dispatch agent sessions are not grouped coherently by initiative/project. For example, a hackathon that spawned 32 dispatch agents across a single day all show up with generic prompts like "You have a plan file at .dispatch/tasks/.../plan.md" and get diluted across unrelated categories in the insights report.

The session metadata already includes project_path, start_time, and first_prompt, but there's no way to tag sessions with a higher-level initiative or label.

Proposed Solution

Add an optional --tag or --label parameter to dispatch (and potentially to claude CLI directly) that gets written into session metadata:

# Tag all dispatched agents with an initiative name
dispatch --tag "hackathon-forge-audit" sonnet to scan repos

# Or at the CLI level
claude --tag "hackathon" -p "do something"

Then /insights could use these tags to group sessions into coherent initiatives, even when the individual session prompts are generic plan-file executions.

Why This Matters

Power users who dispatch many parallel agents for a single initiative (e.g., scanning 3,875 repos, categorizing 428 defects) get their most impressive work invisible in insights because the clustering LLM can't infer that 32 generic dispatch sessions belong together.

Workaround

None currently. Sessions are clustered purely by LLM analysis of prompts and tool usage, which doesn't capture initiative-level grouping.