The terminal's issue screen says what an issue waits for, and `w` adds or removes a wait, as MCP `wait_for` does #7234

For: the owner reshapes the plan from the terminal. Which issue waits for which is the map, and today only the page and MCP can change it.

linkIssue and unlinkIssue (src/actions/dependencies.ts:45 and :76) are reached from the issue page and MCP wait_for. src/tui/screens/issue.ts neither shows nor changes them.

Done:

• [ ] The issue screen shows one line, "Waits for #12, #15" and "Holds up #20", when there are any. Each number opens that issue.
• [ ] For a writer, w asks for an issue number. A new number links it. A number it already waits for asks a confirm, then unlinks it. Refusals (a pull, another repository's issue, a cycle) read in dependencyWords' words.
• [ ] A new test/tui-issue-waits.test.ts covers: link, the line shows it, unlink after a confirm, a pull number refused, and a reader without w.

Files: src/tui/screens/issue.ts, one test. Risk: low.