docs: migrate reminder/gateway/crash-watch/migrate prose to docs (#715)

hive-c0re/src/agent_ports.rs

@@ -1,33 +1,7 @@
-//! `/var/lib/hyperhive/agent-ports.json` writer. Port map for
-//! per-agent `/agent/<name>/` TCP routing. Written alongside
-//! `agents.conf` (see `gateway_nginx.rs`) on every topology change;
-//! `gateway_nginx::render` reads it indirectly via
-//! `lifecycle::agent_web_port` to populate TCP upstreams for agents
-//! that haven't opted in to unix-socket mode yet. Also kept as a
-//! human-readable audit file — `cat agent-ports.json` shows every
-//! registered sub-agent and its deterministic port assignment.
-//!
-//! Shape (flat object keyed by logical agent name → web port):
-//!
-//! ```json
-//! {
-//!   "iris":     8178,
-//!   "atlas":    8304,
-//!   "argus":    8267,
-//!   "damocles": 8549
-//! }
-//! ```
-//!
-//! Ports come from [`crate::lifecycle::agent_web_port`] — pure
-//! FNV-1a(name) hash so the value is reproducible from the name
-//! alone. Manager is excluded from the map: the gateway routes `/`
-//! straight to it via the c0re dashboard upstream rather than a
-//! per-agent `/agent/<name>/` prefix.
-//!
-//! Atomicity: write to a sibling `.tmp` file + rename so a partial
-//! write never leaves an unparseable file in place. The gateway's
-//! `nginx` worker can read mid-write and Just Work because `rename()`
-//! is atomic on the same filesystem.
+//! `/var/lib/hyperhive/agent-ports.json` writer — flat map of
+//! agent name → TCP web port. Written alongside `agents.conf` on
+//! every topology change. JSON shape, port derivation (FNV-1a hash),
+//! atomicity, and manager exclusion: `docs/gateway.md::Agent port map`.
 
 use std::collections::BTreeMap;
 use std::path::PathBuf;