v0.7.0: multiple tasks per workspace + dashboard redesign

[marioolf]

v0.7.0 — Multiple tasks per workspace

A workspace can now hold several independent Claude sessions ("tasks") that share the same project directory — parallel efforts in one repo without cloning it.

• Model: project.Task + Project.Tasks. Named tasks get crabby_<workspace>_<task> sessions (generated automatically); the default main task keeps the legacy crabby_<workspace> name.
• Migration: existing single-session registries migrate in-memory to a default main task on their original session — existing workspaces keep working, no action needed.
• Commands: crabby task create/list/delete/restart; crabby attach [workspace] [task] asks which task when several exist (or pass the name).
• Dashboard: tasks are grouped under their workspace; a header row for multi-task workspaces; t starts a new task; navigation skips headers.

Dashboard redesign

• Banner stays centred; the list and footer are left-aligned like a normal CLI, with each row's live data in a column to the right of its name.
• Footer action keys are highlighted (accent colour) so they read distinctly from the informational usage summary.

Notes

• Task status is derived live from tmux, never stored.
• With several tasks sharing one directory, transcript-derived detail (model/tokens/activity) shows at the workspace level; per-task rows show reliable tmux state, since Claude transcripts can't be attributed to a specific tmux session.