refactor(cli): self-declared agent_caller via --agent-caller flag

Switch agent identity from env-var sniffing to explicit self-declaration
(Proof Editor-style). The agent now passes its own name when running
mem0 init --agent --agent-caller <name>.

Why: env-var detection was speculative for everything but Claude Code —
CLAUDECODE=1 is documented and verified, but CURSOR_AGENT, CODEX_CLI,
CLINE_AGENT etc. were plausible-sounding picks without upstream
confirmation. Self-declaration is honest, future-proof (no whitelist
treadmill as new agents emerge), and matches how Proof handles agent
join: explicit identity from the agent itself.

CLI changes:
- New --agent-caller <name> option on `mem0 init` (Python + Node)
- Removed detect_agent_caller() as the source for agent_caller field;
  still used as a context trigger ("does this look like an agent?")
  for Rule 3 auto-bootstrap and for telemetry-only event property —
  identity goes to NULL unless --agent-caller is passed
- runInit / run_init accept agent_caller kwarg, forward to backend
- PostHog cli.init event uses the self-declared value (not env-sniffed)

Companion backend change (mem0ai/platform#2784) drops the whitelist
normalizer for an open sanitize so any sensible name is accepted.

cli/node/src/commands/init.ts

@@ -270,6 +270,7 @@ export async function runInit(
 		force?: boolean;
 		agent?: boolean;
 		source?: string;
+		agentCaller?: string;
 	} = {},
 ): Promise<void> {
 	const { detectAgentCaller } = await import("../agent-detect.js");
@@ -282,8 +283,8 @@ export async function runInit(
 		claimed = false,
 	) => {
 		const props: Record<string, unknown> = { command: "init", mode };
-		const caller = detectAgentCaller();
-		if (caller) props.agent_caller = caller;
+		// Self-declared via --agent-caller; not sniffed from env vars.
+		if (opts.agentCaller) props.agent_caller = opts.agentCaller;
 		if (opts.source) props.signup_source = opts.source;
 		if (claimed) props.claimed_agent_mode = true;
 		captureEvent("cli.init", props);
@@ -367,9 +368,13 @@ export async function runInit(
 			return;
 		}
 		// Rule 3: mint a fresh shadow (no valid key to reuse).
+		// agent_caller is self-declared via --agent-caller (Proof Editor-style),
+		// not derived from env-var sniffing. detectAgentCaller() above is still
+		// used as a context trigger (does this look like an agent?) but never
+		// to fill identity.
 		await bootstrapViaBackend(config, {
 			source: opts.source ?? null,
-			agentCaller: detectAgentCaller(),
+			agentCaller: opts.agentCaller ?? null,
 		});
 		fireInit("agent");
 		return;

cli/node/src/index.ts

@@ -220,6 +220,10 @@ program
 		"--source <channel>",
 		"Channel attribution for signup (e.g. github, hn, ph).",
 	)
+	.option(
+		"--agent-caller <name>",
+		"Self-declared agent identity (e.g. claude-code, cursor). Used with --agent to attribute Agent Mode signups.",
+	)
 	// Accept `--json` at the init level too so the PRD-documented form
 	// `mem0 init --agent --json` works without requiring users to move it
 	// before the subcommand. Effect is identical to the global `--json`:
@@ -242,6 +246,7 @@ program
 			force: opts.force,
 			agent: opts.agent,
 			source: opts.source,
+			agentCaller: opts.agentCaller,
 		});
 	});