APP-93: Simplify the Truffile agent setup prompt

[temp-deepshard]

Why

The installation page should let a user hand an existing coding agent one Truffle goal. The agent should handle setup and local work, then pause only at a real human or device boundary.

Changes

• replaces the long procedural prompt with a short goal-first prompt
• tells the agent to install or upgrade Truffile, load only relevant copied skills, run doctor, and continue device-independent work
• tells the agent not to ask the user to paste commands it can run itself
• names the human boundaries: Symphony onboarding, physical approval, credentials, deployment, and destructive actions

Validation

• exact APP-93 commit 8e160f4
• official Mint strict validation passed
• isolated agent flow installed the wheel, loaded resources, diagnosed the no-device state, and continued through create, validate, and deploy dry-run
• automated CI: none configured; validation was run manually

Depends on: #6 and deepshard/truffile#41 through #45

Review note

GitHub cannot set this PR's base to a branch that exists only on the contributor fork. Until #6 merges, this PR's Files tab also shows the #6 parent commit. Review #6 first; after it lands, this PR reduces to the single APP-93 prompt commit.

Linear: APP-93