fix(aider): CONVENTIONS.md is a roster index, not 3.8 million characters of agents (#871)

Aider loads a conventions file into context and keeps it there for the whole
session — that is what the file is for, and the docs say to load it with
--read so prompt caching can hold it. This integration concatenated every
agent body into it. At 279 agents that is 3,816,372 characters, roughly a
million tokens. No model takes that. Anyone who ran

    ./scripts/install.sh --tool aider

got a CONVENTIONS.md that either blows the context window on the first turn
or bills for a million tokens trying.

CONVENTIONS.md is now the roster index it was described as: one entry per
agent with the name, the description, the division, and the path to the
agent file. 96,823 characters, down from 3.8 million. The header explains
how to pull a single agent's full instructions into the session:

    /read-only /path/to/agency-agents/engineering/engineering-frontend-developer.md

Naming an agent in a prompt still works the way it did — the description is
what the model needed for that, and it is still there.

test-convert-outputs.sh now holds the index to being an index: it fails if
CONVENTIONS.md grows past 250,000 characters, if it does not list exactly
one path per roster agent, or if any path it prints does not resolve. The
existing round-trip check on the accumulated file still covers the names and
descriptions.

integrations/README.md

@@ -12,7 +12,7 @@ supported agentic coding tools.
 - **[OpenCode](#opencode)** — `.md` agent files in `opencode/`
 - **[OpenClaw](#openclaw)** — `SOUL.md` + `AGENTS.md` + `IDENTITY.md` workspaces
 - **[Cursor](#cursor)** — `.mdc` rule files in `cursor/`
-- **[Aider](#aider)** — `CONVENTIONS.md` in `aider/`
+- **[Aider](#aider)** — `CONVENTIONS.md` roster index in `aider/`
 - **[Windsurf](#windsurf)** — `.windsurfrules` in `windsurf/`
 - **[Kimi Code](#kimi-code)** — YAML agent specs in `kimi/`
 - **[Qwen Code](#qwen-code)** — project-scoped `.md` SubAgents in `.qwen/agents/`
@@ -171,8 +171,10 @@ See [cursor/README.md](cursor/README.md) for details.
 
 ## Aider
 
-All agents are consolidated into a single `CONVENTIONS.md` file that Aider
-reads automatically when present in your project root.
+`CONVENTIONS.md` is the roster index — name, description, and the path to each
+agent's full instructions. Aider keeps a conventions file in context for the
+whole session, so the file lists the agents instead of inlining a million
+tokens of them.
 
 ```bash
 cd /your/project && /path/to/agency-agents/scripts/install.sh --tool aider