feat(dashboard): add ticket workflow control plane

[jiunbae]

Summary

• replace the always-expanded tmux hierarchy with a workspace rail and five-stage ticket board
• prefer Muxa-managed workspace/work/agent identities and infer legacy workspaces from repository cwd
• add a PAT-gated work drawer with durable title, goal, next-action, and workflow metadata
• add exact-ticket batch prompt/status/abort controls while preserving Fleet dashboard routes
• keep session/window/pane topology available as secondary execution diagnostics

Validation

• cargo fmt --all -- --check
• node --check crates/muxa/src/dashboard/web/main.js
• node --test crates/muxa/tests-js/dashboard-work-model.test.mjs
• cargo build -p muxad
• cargo test --workspace --no-fail-fast
• cargo clippy --workspace --all-targets -- -D warnings