fix(cli): add -u short form to lsp add --update

Add the missing `-u` short-form alias for the `--update` option on the
`lsp add` command, aligning the implementation with the specification
(spec line 8645: `agents lsp add [--update|-u] (--config|-c) <FILE>`).

The Typer option declaration in `lsp.py` now includes `"-u"` alongside
`"--update"`.  A new Behave scenario ("Add LSP server with -u short form
overwrites existing") and its step definition verify the short form works
end-to-end through the CLI runner.

No conflicts exist — `-u` was not claimed by any other option on
`lsp add` (existing short forms: `-c` for `--config`, `-f` for
`--format`).

ISSUES CLOSED: #912

features/lsp_cli_new_coverage.feature

@@ -39,6 +39,14 @@ Feature: LSP CLI commands coverage
     Then the lsp CLI command should succeed
     And the lsp CLI output should contain "LSP Server Registered"
 
+  @lsp_cli_add
+  Scenario: Add LSP server with -u short form overwrites existing
+    Given a valid LSP server YAML config file
+    And the LSP server has been registered via CLI
+    When I run lsp CLI add with --config and -u short form
+    Then the lsp CLI command should succeed
+    And the lsp CLI output should contain "LSP Server Registered"
+
   @lsp_cli_add
   Scenario: Add LSP server with --format json
     Given a valid LSP server YAML config file

features/steps/lsp_cli_new_coverage_steps.py

@@ -218,6 +218,13 @@ def step_run_lsp_add_update(context: Context) -> None:
     )
 
 
+@when("I run lsp CLI add with --config and -u short form")
+def step_run_lsp_add_u_short(context: Context) -> None:
+    context.lsp_cli_result = _runner.invoke(
+        app, ["add", "--config", context.lsp_yaml_path, "-u"]
+    )
+
+
 @when("I run lsp CLI add with --config and --format json")
 def step_run_lsp_add_json(context: Context) -> None:
     context.lsp_cli_result = _runner.invoke(

src/cleveragents/cli/commands/lsp.py

@@ -122,6 +122,7 @@ def add(
         bool,
         typer.Option(
             "--update",
+            "-u",
             help="Allow overwriting an existing LSP server registration",
         ),
     ] = False,