Spec #135: owner data-correction actions — Latest Chapter, series_url, Cover, orphan removal (#156)

Implements spec #135 (spec 2 of 4, derived from wayfinder map #114; decisions settled in #120/#121/#125/#131). Blocked-by #134 is merged, so this lands on `main`.

Four owner actions the dashboard can now perform, one ticket each:

- **#149** — Latest Chapter correction: one numeric input, overwritten by the next machine write.
- **#151** — Series URL repair: owner-typed, gated by the poller's own fetch gate.
- **#150 / #153 / #154** — Cover replacement: addresses derived from bytes (`#150`), a Forced Poll replaces the Cover while an ordinary pass still only fills a blank one (`#153`), and byte reclamation is one guarded helper, file first / covers row last (`#154`).
- **#155** — Orphan removal: one Series at a time, with the foreign key as the guard.

Plus **#152** — Latest Chapter provenance: one derived line naming the actor class, so an owner can tell a hand-edited number from a machine read.

- Migration `0015_latest_correction.sql` adds the correction/provenance columns; `0009` now derives cover addresses from bytes.
- ADR `0014-cover-addresses-from-bytes.md` records the address scheme.

Backend tests cover the store, poller, admin handlers, and web routes (`go test ./...`, needs Docker).

Reviewed-on: #156
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

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.