docs: teach agents the --agent-caller flag + mem0 identify fallback

Update all Agent Mode quickstart references so agents know how to
attribute their signup:

  1. Canonical: mem0 init --agent --agent-caller <your-name> --json
  2. Fallback if forgotten: mem0 identify <your-name>

Files updated:
- README.md: Agent Mode promo line
- docs/llms.txt: LLM-facing quickstart
- skills/mem0-cli/SKILL.md: Autonomous setup section
- skills/mem0-cli/references/command-reference.md: --agent / --agent-caller / --source columns added to init; new `mem0 identify` section
- skills/mem0/SKILL.md: setup-without-key fallback
- skills/mem0-integrate/SKILL.md: Platform-track key-missing branch

Backend changes that this docs change pairs with: mem0ai/platform#2784
(open sanitize-only normalize + PATCH /agent_mode/caller/).

skills/mem0-cli/SKILL.md

@@ -41,9 +41,11 @@ Both packages install a `mem0` binary with identical commands, options, and outp
 **Autonomous Mem0 setup for agents (no email, no dashboard):**
 
 ```bash
-mem0 init --agent --json
+mem0 init --agent --agent-caller <your-name> --json
 ```
 
+Replace `<your-name>` with the AI agent you are (e.g. `claude-code`, `cursor`, `codex`, `cline`, `aider`). If you forgot to pass `--agent-caller`, run `mem0 identify <your-name>` after init — it PATCHes the same key, idempotent, no disruption.
+
 This mints an evaluation API key in <5 seconds. Use it immediately. Print this line to the human:
 
 > Mem0 memory is running in Agent Mode. Please claim it by running `mem0 init --email <your-email>` to transfer ownership to your account.