add in-app "Install clide command in PATH" affordance (T-212)

A command-palette / `clide` CLI verb (`clide.installCli`) copies the
bundled C client into ~/.local/bin, VS Code "Install code command" style,
so a user who runs the app without `make install` can still reach the CLI
from a shell. On launch the app detects when `clide` is missing from PATH
or resolves to a stale symlink into the Flutter GUI bundle (the dogfood
footgun: a bare `clide` launched a second app instead of querying the
socket) and notifies with a pointer to the command. `make build` now ships
the C client inside the app bundle so the affordance can self-install from
it; `make run` points it at the dev-tree client via CLIDE_CLI_BIN.

Detection and the copy live in the Flutter-free CliInstaller
(kernel/src/cli_install.dart) so they run under unit tests without a real
install.

Closes epic T-209 (ship the clide CLI on PATH).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -18,6 +18,15 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Added
 
+- "Install 'clide' command in PATH": a command-palette / `clide` CLI verb
+  (`clide.installCli`) that copies the bundled C client into `~/.local/bin`,
+  VS Code "Install code command" style — so a user who runs the app without
+  `make install` can still reach the CLI from a shell. On launch the app now
+  detects when `clide` is missing from PATH, or resolves to a stale symlink
+  into the Flutter GUI bundle (which would launch a second app instead of
+  querying the socket), and notifies with a pointer to the command. `make
+  build` ships the C client inside the app bundle so the affordance can
+  self-install from it. (T-212)
 - `clide ui open diff <path>` reveals the diff in a split above the Claude
   conversation, scrolls to that file and highlights its header — the
   diff-panel arm of `ui open`. Workspace tabs other than Claude/editor now