Remove deprecated watch command

[LarsCowe]

Context

bmalph watch was deprecated in favor of bmalph run in 4da6764. It currently prints a deprecation warning to stderr but still functions normally.

What to remove

• src/commands/watch.ts — delete file
• src/cli.ts — remove watch command registration and import
• slash-commands/bmalph-watch.md — delete file
• tests/commands/watch.test.ts — delete file
• tests/e2e/watch.e2e.test.ts — delete file
• tests/e2e/helpers/cli-runner.ts — remove runWatch helper
• README.md — remove watch from feature list, CLI table, and options section
• CLAUDE.md — remove watch from feature list and CLI table

The src/watch/ module (renderer, state-reader, file-watcher, types) must be kept — bmalph run imports from it.