Add Kimi Code's default install path to managed-agent binary discovery (#5997)

## Summary

Buzz Desktop fails to detect a freshly-installed Kimi Code CLI, even
though `kimi --version` works fine in the terminal. Root cause is in
binary discovery, not in Kimi's install.

## Problem

After running Kimi Code's installer, Buzz Desktop's harness list doesn't
pick up the `kimi` binary — it stays undetected until the user manually
sources their shell config.

## Repro

1. Install Kimi Code: `curl ... code.kimi.com/kimi-code/install.sh |
bash` — installs to `~/.kimi-code/bin`, and the installer appends a PATH
export only to `~/.zshrc`.
2. Open a fresh terminal or restart Buzz Desktop without `source
~/.zshrc`.
3. Buzz Desktop does not detect `kimi`, even though it's on disk and
executable.

## Root cause

`find_via_login_shell()` in
`desktop/src-tauri/src/managed_agents/discovery.rs` resolves binaries by
spawning `zsh -l -c 'command -v <bin>'`. A login shell sources
`~/.zprofile`/`~/.zshenv`, but zsh only sources `~/.zshrc` for
*interactive* shells — so a PATH export that lives only in `~/.zshrc`
(which is where Kimi's installer puts it) is invisible to this probe.
`~/.kimi-code/bin` is also absent from the static fallback list in
`common_binary_paths()`.

This is the same root-cause class already handled for `nvm` in this file
(see the `find_nvm_default_bin` comment) — Kimi just doesn't have an
equivalent fallback yet.

## Fix

Add `~/.kimi-code/bin` to the Unix branch of `common_binary_paths()`,
alongside the existing `.volta/bin` / `.bun/bin` / `.asdf/shims`
entries.

## Scope note

This PR only fixes detection (finding the binary). It does not address
that Kimi shows a "Ready" badge regardless of login status — that's a
separate, larger gap affecting all five preset harnesses (Kimi,
OpenCode, Amp, Hermes, OpenClaw), tracked separately.

## Test plan

- [x] `just ci` passes
- [x] Manual: fresh Kimi install per repro steps above, confirm Buzz
Desktop shows it without sourcing `~/.zshrc`

Signed-off-by: Shawn Hank <shawn@shawnhank.com>

desktop/src-tauri/src/managed_agents/discovery.rs

@@ -61,6 +61,7 @@ fn common_binary_paths() -> &'static [PathBuf] {
                 home.join(".volta/bin"),
                 home.join(".asdf/shims"),
                 home.join(".bun/bin"),
+                home.join(".kimi-code/bin"),
             ]);
         }
         // Windows well-known dirs for npm global shims and standalone installer targets.