Discover feeds behind aggregator-only articles

A best-effort pipeline stage after social enrichment asks Miniflux to
discover the feeds behind each aggregator-only article, validates every
result by sniffing the body, and records the survivors as feed candidates
with a per-host memo. Ranking is a shrunk mean over the linked articles'
existing telemetry and ratings. `daily-epub feeds discover` runs the same
pass over recent articles for seeding.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QVPagF6jfDv78CC5Jv2wp4

migrations/0010_feed_discovery.sql

@@ -0,0 +1,27 @@
+-- Feed discovery: proposed Miniflux subscriptions found behind aggregator-only
+-- articles (feed discovery plan §4 step 1).
+
+CREATE TABLE feed_candidates (
+    id               INTEGER PRIMARY KEY AUTOINCREMENT,
+    feed_url         TEXT NOT NULL UNIQUE,
+    host             TEXT NOT NULL,
+    title            TEXT,
+    status           TEXT NOT NULL CHECK (status IN ('candidate', 'added', 'dismissed')),
+    first_seen       TEXT NOT NULL,
+    last_seen        TEXT NOT NULL,
+    miniflux_feed_id INTEGER,
+    decided_at       TEXT
+);
+CREATE INDEX idx_feed_candidates_status_host ON feed_candidates(status, host);
+
+CREATE TABLE feed_candidate_articles (
+    candidate_id INTEGER NOT NULL REFERENCES feed_candidates(id) ON DELETE CASCADE,
+    article_id   INTEGER NOT NULL REFERENCES articles(id) ON DELETE CASCADE,
+    PRIMARY KEY (candidate_id, article_id)
+);
+
+CREATE TABLE feed_discovery_hosts (
+    host       TEXT PRIMARY KEY,
+    checked_at TEXT NOT NULL,
+    candidates INTEGER NOT NULL
+);