fix: unify status-bar field keys, docs, and tests for salvaged cluster

Follow-up to the cherry-picked #41909/#92696 + #39760 + #97970 cluster:
- single field-key namespace (display.status_bar.fields) instead of the
  second tui_statusbar_fields list; cache_hit/latency/tps/stash/battery/
  title join the existing key set
- cache-hit % prefers the baseline-delta regime (resets on model switch
  and compression) and hides on zero cache reads instead of alarming 0%
- latency/tps segments added to the styled fragment renderer too
- docs updated in website/docs/user-guide/configuration.md
- 7 new tests: rolling latency/t/s, NaN/negative guard, field filtering,
  baseline resets, title badge gating

cli.py

@@ -6546,16 +6546,17 @@ class HermesCLI(CLIAgentSetupMixin, CLICommandsMixin, CLIBillingMixin):
                 base_read = cur_read
             delta_prompt = cur_prompt - base_prompt
             delta_read = cur_read - base_read
-            if delta_prompt > 0 and delta_read >= 0:
-                pct = int(round((delta_read / delta_prompt) * 100))
-                pct = max(0, min(100, pct))
+            # A zero-read regime hides the segment entirely (no cache data
+            # is not the same as a 0% hit worth alarming about), and the pct
+            # stays a float so renderers control their own precision.
+            if delta_prompt > 0 and delta_read > 0:
+                pct = max(0.0, min(100.0, (delta_read / delta_prompt) * 100))
                 snapshot["cache_hit_pct"] = pct
-                snapshot["cache_hit_label"] = f"{pct}%"
-            elif cur_prompt > 0 and cur_read >= 0 and base_prompt == 0 and base_read == 0:
-                pct = int(round((cur_read / cur_prompt) * 100)) if cur_prompt else 0
-                pct = max(0, min(100, pct))
+                snapshot["cache_hit_label"] = f"{pct:.0f}%"
+            elif cur_prompt > 0 and cur_read > 0 and base_prompt == 0 and base_read == 0:
+                pct = max(0.0, min(100.0, (cur_read / cur_prompt) * 100))
                 snapshot["cache_hit_pct"] = pct
-                snapshot["cache_hit_label"] = f"{pct}%"
+                snapshot["cache_hit_label"] = f"{pct:.0f}%"
             else:
                 snapshot["cache_hit_pct"] = None
                 snapshot["cache_hit_label"] = ""