docs(forge): define concept taxonomy

[fronzec]

Closes #20

Type

• Documentation only

Summary

• Define a bounded, concept-first taxonomy for current and future Forge experiments.
• Require agents to reuse existing concepts and obtain approval before creating a new one.
• Simplify and order the root experiment catalog while linking the canonical guidelines.

Changes

File	Change
docs/concepts.md	Define placement rules, seven target concepts, exclusions, anti-patterns, and migration boundaries.
AGENTS.md	Require concept evaluation, ordered catalog updates, and use of the documentation guidelines.
README.md	Add Forge branding, link the guidelines, remove the status column, and order experiments by concept.

Verification

• git diff --check
• All scoped Markdown links resolve.
• All 17 current experiments are mapped exactly once.
• Independent documentation audit passed.
• Native review receipt validated at pre-commit, pre-push, and pre-PR gates.
• Runtime verification: N/A — documentation and agent guidance only.

Contributor checklist

• Linked approved issue docs: define Forge concept taxonomy #20.
• Uses exactly one type:* label: type:docs.
• No shell scripts changed; ShellCheck is not applicable.
• Documentation skills were loaded and exercised.
• Conventional commit used with no AI attribution.