feat: agent-driven setup — flatten rules, drop the manual steps

As AI agents get better at following instructions, it opens up simpler
ways to solve problems we used to handle with scripts and commands.

Rather than maintaining platform-specific setup steps for every IDE,
we now provide a single prompt and let the agent create the right
config file for its environment.

Flattened aidlc-rules/ into one directory. Added SETUP.md with a
two-step process: git submodule add, then paste the prompt. The agent
handles the rest.

Author: David Hache

CONTRIBUTING.md

@@ -10,19 +10,21 @@ Before contributing, familiarize yourself with our [tenets](README.md#tenets).
 
 ## Contributing Rules
 
-AI-DLC rules live in `aidlc-rules/aws-aidlc-rule-details/`. When contributing:
+AI-DLC rules live in `aidlc-rules/`. When contributing:
 
-- **Be reproducible**: Changes should be consistently reproducible either via test case or a series of step
+- **Be reproducible**: Changes should be consistently reproducible either via test case or a series of steps.
 - **Single source of truth**: Don't duplicate content. If guidance applies to multiple stages, put it in `common/` and reference it.
 - **Keep it agnostic**: The core methodology shouldn't assume specific IDEs, agents, or models. Tool-specific files are generated from the source.
 
 ### Rule Structure
 
-Rules are organized by phase:
+Rules are organized by phase under `aidlc-rules/`:
+- `core-workflow.md` - The main workflow entry point
 - `common/` - Shared guidance across all phases
 - `inception/` - Planning and architecture rules
 - `construction/` - Design and implementation rules
 - `operations/` - Deployment and monitoring rules
+- `extensions/` - Optional cross-cutting constraint rules
 
 ### Testing Changes