Add Indico agent guidelines and skills

[moliholy]

This PR imports shared agent guidance from unconventionaldotdev/indico-agents as a submodule under agents/indico, and exposes its universal markdown files at host-native paths via relative symlinks.

Overview

The submodule ships:

• AGENTS.md and CODING_GUIDELINES.md: shared baseline for any Indico-based host repository.
• indico/AGENTS.md: guidance for editing files inside the upstream Indico submodule.
• skills/: reusable agent skills (locate, RHs, migrations, tests, submodule bumps) consumable by any AI assistant that reads SKILL.md files.
• scripts/install-links.sh: bootstrap that materialises symlinks idempotently.

indicorp/
├── AGENTS.md             -> agents/indico/AGENTS.md             (committed)
├── CODING_GUIDELINES.md  -> agents/indico/CODING_GUIDELINES.md  (committed)
├── indico/
│   └── AGENTS.md         -> ../agents/indico/indico/AGENTS.md   (per-clone, gitignored upstream)
├── .claude/skills/...    -> ../../agents/indico/skills/...      (per-contributor, gitignored)
└── agents/indico/        (submodule)

Universal symlinks are committed once. Skill symlinks are per-contributor: each teammate may use a different assistant (Claude Code, Codex, Cursor), so the chosen */skills/ directory is gitignored.

How to test

After cloning or pulling:

git submodule update --init --recursive

# Universal markdown (AGENTS.md, CODING_GUIDELINES.md, indico/AGENTS.md)
bash agents/indico/scripts/install-links.sh

# Plus skills for your AI assistant of choice
bash agents/indico/scripts/install-links.sh .claude/skills    # Claude Code
bash agents/indico/scripts/install-links.sh .codex/skills     # OpenAI Codex
bash agents/indico/scripts/install-links.sh .cursor/skills    # Cursor

Verify:

• readlink AGENTS.md resolves to agents/indico/AGENTS.md.
• readlink indico/AGENTS.md resolves to ../agents/indico/indico/AGENTS.md.
• git -C indico status is clean (the host-side symlink is added to the upstream submodule's local .git/info/exclude).
• ls .claude/skills/ shows each shared skill as a directory symlink, and they do not appear in git status (covered by .gitignore).

See agents/indico/HOST_INTEGRATION.md for the full integration model.

[OmeGak]

There is no indication anywhere in the repo (other than the comment in .gitignore that a developer can install agent skills by running agents/indico/scripts/install-links.sh. Let's make this easier by:

1. Adding a target in Makefile
2. Documenting the fact that the repo is agent-enabled in README.md

[moliholy]

Both points were already in before your review landed: make agent-skills (plus a help entry under an "Agents" section) and a "Using AI agents" section in README.md pointing at the target and at AGENTS.md.

The rest of the feedback is addressed now. CLAUDE.md and CONVENTIONS.md come from the submodule, so this PR carries a pointer bump against unconventionaldotdev/indico-agents#2. I will re-bump to the squashed commit once that one merges.

Ready for another round.

[OmeGak]

LGTM 🤖