Series URL repair: owner-typed, gated by the poller's own fetch gate (#151)

AGENTS.md

@@ -99,7 +99,7 @@ Go backend:
 
 - SQL always parameterized (`$N`). Only compile-time constants (`bookmarkColumns`) may be concatenated into query text — never a request value, not even a validated one.
 - `html/template` only for anything a browser parses, never `text/template`. Never wrap stored or fetched strings in `template.HTML`/`JS`/`URL`; that switches off the escaping every template depends on.
-- Any outbound fetch of a client-supplied URL passes `fetchableSeriesURL` (site + `https` + host check) first. `series_url` arrives in a PUT body, so without the gate the poller will probe arbitrary hosts from the server's own network position. New fetch path reuses the gate rather than re-deriving one.
+- Any outbound fetch of a client-supplied URL passes `FetchableSeriesURL` (site + `https` + host check) first. `series_url` arrives in a PUT body, so without the gate the poller will probe arbitrary hosts from the server's own network position. New fetch path reuses the gate rather than re-deriving one.
 - Cap every remote body with `io.LimitReader` (`maxBodyBytes`). An unbounded read is an OOM handed to whatever is on the other end.
 - Compare secrets with `hmac.Equal` / `subtle.ConstantTimeCompare`, never `==`. A credential is matched by the SHA-256 the `readers` table holds, which is already a fixed-width equality — a new secret comparison must not regress to `==`.
 - Errors: generic text to the client (`http.Error(w, "internal error", 500)`), detail to `log.Printf`. Never log `TOKEN_KEY`, a Reader's credential, `DISCORD_CLIENT_SECRET`, a session id, or a whole `Authorization` header.