fix(dev): allow full project-context usage with conflict precedence

[alexeyv]

Summary

• Fixes unintended consequence where dev agent ignored half of project-context.md
• Changes wording from "for coding standards only" to "follow its guidance; when conflicts exist, story requirements take precedence"
• Updates 3 places: 2 in principles, 1 in critical_actions

Fixes #1132

Problem

The original wording (from Nov 23 Phase 4 transformation) was:

"Load project-context.md if available for coding standards only - never let it override story requirements"

This caused agents to preemptively ignore legitimate project-context guidance (architecture patterns, dependencies, conventions) even when it didn't conflict with the story.

Solution

New wording establishes clear hierarchy without limiting scope:

"Load project-context.md if available and follow its guidance - when conflicts exist, story requirements always take precedence"

Tested

Created test scenario with contradicting project-context and story, validated that agent:

• Reads ALL of project-context.md (doesn't skip sections
• Correctly identifies conflicts
• Defers to story requirements on all 4 conflicts
• Explains reasoning (architect approval, migration context, etc.)

Test plan

• Schema validation passes
• Manual test: agent correctly resolves conflicts in favor of story
• Manual test: agent still reads and applies non-conflicting project-context guidance
• Tested on multiple LLMs with same prompt - all produce correct behavior
  EOF
  )