The planner's brief names the files that are hot now, with their pull counts, so it plans around them #7428

Intent: the planner stops opening issues the forge will hold. Three planning runs today opened issues on src/tui/forge.ts, src/cli/main.ts and docs/MCP.md that were held as soon as they opened.

Done:

• [ ] A planner's brief (src/crew/brief.ts) gets one line: Hot now (an issue whose Files: line names one waits): src/tui/forge.ts=5 src/cli/main.ts=5 …. It uses hotFiles and hotWords from src/crew/hot_files.ts, at most 10 files, hottest first, and is left out when nothing is hot.
• [ ] Builders' briefs are unchanged.
• [ ] A test (e.g. test/brief-hot.test.ts) remembers pull files that make two paths hot and checks the planner brief has the line in order, a builder brief does not, and no line appears when nothing is hot.

Files: src/crew/brief.ts, a new test.