refactor(beads): drop local beads-rust extension in favor of upstream task storage

Local beads was a side project for task tracking layered on the
beads_rust SQLite store. Upstream jcode solves the same problem with
plain file-backed JSON under ~/.jcode/{goals,todos}/, reusing the
shared types in jcode-task-types. Remove the local extension to align
with upstream and avoid carrying a private SQLite-backed dependency.

* Remove crates/jcode-beads-bridge (4 .rs files).
* Remove crates/jcode-app-core/src/tool/beads.rs and the six
  beads_* tool registrations in tool/mod.rs.
* Remove crates/jcode-base/src/beads.rs and its pub mod entry.
* Rewrite crates/jcode-base/src/goal.rs to re-export
  jcode_task_types::{Goal, GoalMilestone, GoalScope, GoalStatus,
  GoalStep, GoalUpdate} and store goals as JSON in
  ~/.jcode/goals/ (global) or <working_dir>/.jcode/goals/
  (project), with per-session attachments in
  ~/.jcode/goals/attachments/<session>.json. Behavior mirrors
  upstream jcode-base::goal: load_goal, list_relevant_goals,
  create_goal, update_goal, resume_goal, attach_goal_to_session,
  load_attached_goal, header_badge, render_goals_overview,
  render_goal_detail.
* Rewrite crates/jcode-base/src/todo.rs as a file-backed store at
  ~/.jcode/todos/<session>.json using jcode_task_types::TodoItem.
* Drop the jcode-beads-bridge and beads_rust workspace dependencies,
  the workspace member entry, and the matching entries in
  crates/jcode-base/Cargo.toml.
* Update TUI callers (commands.rs, local.rs) for the typed
  GoalStatus / GoalScope enums instead of String.
* Drop the .beads/ working tree.
* Drop the beads_list / beads_dep entries from the inline
  openers picker.

Author: quangdang46