Merge the caldav and maild sweep (#232)

One shared response-body read cap named. Both daemons wrote 4<<20 as a bare
literal in two files with no reason beside it.

The rest of the brief was refuted. No swallowed error, no drifted comment, no
repeated connect block. The IMAP password is read once from a file, never
logged, and never crosses to core: mailIngester has one method and it takes
mail content. internal/email/imap.go names no STORE, Seen, Move or Delete verb,
so read-only holds.

(V-581)

cmd/mavcaldav/main.go

@@ -188,6 +188,11 @@ func (p *poller) pollOnce(ctx context.Context) {
 	}
 }
 
+// maxResponseBody bounds every CalDAV response this daemon reads (the poller's
+// GET and the renderer's PROPFIND) — a misbehaving or malicious server gets a
+// truncated read, not an unbounded one.
+const maxResponseBody = 4 << 20
+
 // fetchEvents GETs the calendar URL and parses VEVENTs from the iCal response.
 func (p *poller) fetchEvents(ctx context.Context, now time.Time) ([]calendar.Event, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, p.url, nil)
@@ -203,7 +208,7 @@ func (p *poller) fetchEvents(ctx context.Context, now time.Time) ([]calendar.Eve
 	}
 	defer resp.Body.Close()
 
-	body, err := io.ReadAll(io.LimitReader(resp.Body, 4<<20))
+	body, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseBody))
 	if err != nil {
 		return nil, err
 	}

cmd/mavcaldav/render.go

@@ -142,7 +142,7 @@ func (r *renderer) listPublished(ctx context.Context) ([]int64, error) {
 		return nil, err
 	}
 	defer resp.Body.Close()
-	raw, err := io.ReadAll(io.LimitReader(resp.Body, 4<<20))
+	raw, err := io.ReadAll(io.LimitReader(resp.Body, maxResponseBody))
 	if err != nil {
 		return nil, err
 	}