## Why
Summary agents need project-aware access to prior meeting summaries so current summaries can reuse past decisions and context without mutating historical summary notes.

## What Changes
- Add read-only summary-agent tools to list paginated past meeting summaries scoped to the current meeting's projects.
- Add a read-only tool to read a past project meeting summary with the same line-range behavior as other read tools.
- Extend summary-agent search so project-scoped searches include both bound project files and past summary notes for the scoped projects.
- Reject requested project scopes that are not assigned to the current meeting.

## Impact
- Affected specs: `meeting-summary`, `agent-project-tools`
- Affected code: summary tools, summary agent tool registration, summary agent instructions, README