srrdb: persist per-day harvest ledger alongside releases

Add srrdb_log table with composite primary key (day, category) and counters
found, stored, ignored plus run_at.

Replace the release-only persistence path with UpsertAllSrrdbWithDay so releases
and their corresponding srrdb_log row are written in one SQLite transaction.
Preserve existing error handling: rollback reports the release/day that failed,
and commit errors return without writing a dump.

Handle fully ignored days as closed. When every fetched release is skipped by
ignore rules, still write the ledger row with zero stored releases. This prevents
the automatic day walk from endlessly retrying a day whose releases are filtered
out.

Derive and validate the ledger day from the resolved request URI. Missing or
invalid date: segments now fail before database writes. Keep run_at independent
from created_at semantics and continue populating created_at from the run time.

Preserve column and upsert semantics. category continues to use NOT NULL DEFAULT
empty string; status keeps COALESCE behavior on conflict; nfo, content, and
synced_at remain unchanged.

internal/db/srrdb.sql

@@ -36,4 +36,15 @@ CREATE INDEX IF NOT EXISTS idx_srrdb_group
     ON srrdb_releases (group_name);
 
 CREATE INDEX IF NOT EXISTS idx_srrdb_status
-    ON srrdb_releases (status);
+    ON srrdb_releases (status);
+
+CREATE TABLE IF NOT EXISTS srrdb_log
+(
+    day      TEXT NOT NULL,
+    category TEXT NOT NULL,
+    found    INTEGER NOT NULL,
+    stored   INTEGER NOT NULL,
+    ignored  INTEGER NOT NULL,
+    run_at   TEXT NOT NULL,
+    PRIMARY KEY (day, category)
+);