docs: sync documentation with recent code changes

[aheritier]

Addresses documentation gaps for four PRs merged in the last 36 hours.

PR #3728 — /toolset-restart argument auto-completion

• Updated /toolset-restart entry in the slash commands table to document Tab completion, matching the style of /effort and /drop.

PR #3737 — Session browser git repo root grouping

• Rewrote the "Workspace grouping" description in Session Management: grouping is now by git repository root (worktree-aware), not exact current directory. All worktrees of one repo fold under "This workspace"; the header shows the repo root path.

PR #3727 — Sidebar band: usage from startup and team roster

• Updated the sidebar-band description under Sidebar position to mention that token usage is shown from startup (not only after the first message) and that all team agents are listed by name in multi-agent configs.

PR #3738 — Deferred tool fuzzy search

• Added a new "Tool Discovery with search_tool" subsection to the Deferred Tool Loading docs. Explains the search_tool/add_tool built-ins and the fuzzy matching algorithm (subsequence match, e.g. crfil → create_file).

PRs with docs already included (#3722, #3733, #3734, #3735) and bug-fix/revert PRs with no user-visible behavior change (#3736, #3729, #3726) are not covered here.