feat(opencode): leader keybind, explicit unmount on switch, non-wrapping indicator

Three improvements taken from reading the sibling opencode branches
(feat/opencode-extension-abhishek in particular):

- `<leader>m` opens the project picker. Switching is the repeated action and
  typing `/mcpctl` every time is friction; the other two commands stay
  palette-only.

- A switch disconnects before re-adding. `mcp.add` under the same name does
  re-point the tools on its own, but leaves it to opencode whether the previous
  client is closed — and an abandoned one keeps its `mcp-session-id` alive on
  mcplocal, which is exactly what holds a gated project open. Best-effort, so a
  first mount still works.

- The footer label renders `wrapMode="none" truncate`. The home prompt row is
  narrow enough that the default wrap broke `mcpctl:homeautomation` across two
  lines mid-word; clipping the tail of a long name reads far better.

Verified against opencode 1.18.15: ctrl-x m opens the picker, the home footer is
now one line, and a disconnect-then-add switch still lands — the model called
`mcpctl_begin_session` and listed the new project's tools.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BVwuCjuMoA13gmzYEfcrNP

README.md

@@ -215,8 +215,8 @@ This mints (or reuses) the project's gateway token into
 
 Inside opencode:
 
-- `/mcpctl` — **switch project** from a filterable picker; takes effect on the
-  next turn, no restart
+- `/mcpctl` (or `<leader>m`) — **switch project** from a filterable picker;
+  takes effect on the next turn, no restart
 - `/mcpctl-status` — active project, mount state, gateway URL
 - `/mcpctl-skills` — re-sync this project's skills
 - the active project shows as `mcpctl:<project>` in the prompt footer, next to