fix(build): gate implicit routing on delegated outcomes (#2714)

The previous description matched any code change, so coding agents
entered the build workflow for requests that never asked for it —
including git operations that only record existing content (#2708).

Rewrite the description around who owns the edits:

- Auto-trigger when the user hands over an outcome and leaves the
  edits to the agent; a bare story or issue link counts.
- Always trigger on an explicit BMAD request, with no size floor.
- Never volunteer for user-directed interactive edits or for
  version-control operations that record existing work.

Validated with a 26-case routing eval, each case judged in an
isolated context, on two agent platforms; both score 25/25 on the
final wording.

Fixes #2708

src/bmm-skills/ship/bmad-build/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: bmad-build
-description: 'Implement any requirement, story, bug fix, or change request as working code that follows the project''s existing architecture, patterns, and conventions. Use when the user wants to build, fix, tweak, refactor, add, or modify any code, component, or feature'
+description: 'Turns a work item — feature, story, bug fix, change request — into working code, reviewed and verified. Use when the user hands over an outcome and leaves the edits to you; a bare story or issue link counts. Also use whenever the user asks BMAD by name — then any change qualifies, even a tiny fully-specified edit. Do not volunteer for interactive edits the user directs and reviews themselves, or for version-control operations that record existing work without changing it.'
 ---
 
 Run the following command exactly once without changing the current working directory. Replace `{project-root}` with the absolute path to the project root and `{skill-root}` with the absolute path to this skill's directory: