fix(installer): close --tools "" bypass and drop hardcoded tool count

- Replace truthy `if (options.tools)` guard with `!== undefined` in both
  upgrade and fresh-install branches. Empty string now reaches
  _parseToolsFlag and produces the specific "passed empty" error
  instead of falling through to a generic message (fresh-install) or
  being silently ignored (existing-install).
- Drop the hardcoded "42 supported tools" count from the prereqs in
  install-bmad.md so the doc doesn't drift as platform-codes.yaml
  changes.

Addresses augment / coderabbit review on #2346.

docs/how-to/install-bmad.md

@@ -18,7 +18,7 @@ Use `npx bmad-method install` to set up BMad in your project. One command handle
 
 - **Node.js** 20+ (the installer requires it)
 - **Git** (for cloning external modules)
-- **An AI tool** such as Claude Code or Cursor (run `npx bmad-method install --list-tools` to see all 42 supported tools)
+- **An AI tool** such as Claude Code or Cursor (run `npx bmad-method install --list-tools` to see all supported tools)
 
 :::
 

tools/installer/ui.js

@@ -469,7 +469,9 @@ class UI {
       const allTools = [...preferredIdes, ...otherIdes];
 
       // Non-interactive: handle --tools and --yes flags before interactive prompt
-      if (options.tools) {
+      // Use !== undefined so an explicit --tools "" falls through to _parseToolsFlag and
+      // gets a specific "passed empty" error instead of being silently ignored.
+      if (options.tools !== undefined) {
         const selectedIdes = this._parseToolsFlag(options.tools, allKnownValues);
         await prompts.log.info(`Using tools from command-line: ${selectedIdes.join(', ')}`);
         await this.displaySelectedTools(selectedIdes, preferredIdes, allTools);
@@ -546,8 +548,9 @@ class UI {
 
     let selectedIdes = [];
 
-    // Check if tools are provided via command-line
-    if (options.tools) {
+    // Check if tools are provided via command-line.
+    // Use !== undefined so an explicit --tools "" still hits _parseToolsFlag's empty-value error.
+    if (options.tools !== undefined) {
       selectedIdes = this._parseToolsFlag(options.tools, allKnownValues);
       await prompts.log.info(`Using tools from command-line: ${selectedIdes.join(', ')}`);
       await this.displaySelectedTools(selectedIdes, preferredIdes, allTools);