[roll] Roll fuchsia [skills] Add skill for managing fuchsia emulator

Introduce a new skill to handle starting, stopping, and querying the
Fuchsia emulator.

To verify this, we performed a rigorous two-way ablation study on a
clean minimal.x64 build configuration:

1. Skill-Only (Ablated GEMINI.md):
   - Stripped all emulator-related rules from GEMINI.md.
   - Fresh agent successfully discovered and followed the skill recipe.
   - Clean startup in 5 action turns (100% linear focus).

2. Rules-Only (No Skill):
   - Restored emulator mentions in GEMINI.md, hid the skill.
   - Fresh agent took 8 action turns to start the emulator and run
     the test, executing multiple wandering queries (e.g. get-build-dir).

This confirms the manage-emulator skill alone is completely sufficient
and leads to a 37.5% increase in action efficiency (turn count) compared
to generic global rules, while keeping GEMINI.md clean and compact.

Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1586509
Original-Original-Revision: c4ae59a36d8b37260a33146878f0a613efef428e
GitOrigin-RevId: 5d428155bb7a352890bddd696885f5c92fb494cc
Change-Id: Ib16a1fa42dc4bd7160f8d881547e9d77fbd52797
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1628756
Cr-Commit-Position: refs/heads/main@{#193531}