feat(#73): publish trustworthy first usage history

- Schema migration 1-2: add segment_id to samples, unattributed bytes to day_aggregates

- Collector now derives hour observations and day aggregates from sample pairs

- Cross-hour deltas tracked as unattributed (no proportional allocation)

- Display states: 0 samples -> awaiting first, 1 sample -> awaiting another

- Monitoring period ensured open on each collection run

- Derivation failures preserve prior history

Closes #73

src/fenris/tui.py

@@ -447,15 +447,32 @@ class FenrisTuiApp(App):
 
     def _render_all_regions(self, conn: sqlite3.Connection) -> None:
         """Render all four regions from live store data."""
-        # --- Headline band (§7.2) ---
+        # --- Sample count for single-sample state (issue #73 AC3) ---
         try:
-            proj = compute_projection(conn, self._clock_now)
-            headline = self._format_headline(proj)
-            confidence = self._format_confidence(proj)
-            scenario = self._format_scenario(proj)
-            self._render_headline(headline + "\n" + confidence + "\n" + scenario)
+            cursor = conn.execute("SELECT COUNT(*) FROM samples")
+            sample_count = cursor.fetchone()[0]
+            cursor = conn.execute("SELECT COUNT(*) FROM day_aggregates")
+            day_count = cursor.fetchone()[0]
         except Exception:
-            self._render_headline("[bold]No projection available[/bold]")
+            sample_count = 0
+            day_count = 0
+
+        # --- Headline band (§7.2) ---
+        if sample_count <= 1 and day_count == 0:
+            # Single sample: awaiting another sample
+            self._render_headline(
+                "[bold]Awaiting another sample[/bold]\n\n"
+                "Collecting usage data — the first projection requires at least two samples."
+            )
+        else:
+            try:
+                proj = compute_projection(conn, self._clock_now)
+                headline = self._format_headline(proj)
+                confidence = self._format_confidence(proj)
+                scenario = self._format_scenario(proj)
+                self._render_headline(headline + "\n" + confidence + "\n" + scenario)
+            except Exception:
+                self._render_headline("[bold]No projection available[/bold]")
 
         # --- Usage-history pane (§7.2 left) ---
         history = _query_usage_history(conn)