fix(usage): dedup provider-wide notes and add report-level notes field

Provider-wide disclaimers (e.g. OpenCode Go's "OMP-observed spend
only") were duplicated onto every UsageLimit, then repeated N times
in the TUI aggregate renderer (once per account × window). With
2 accounts × 3 windows, the same disclaimer appeared 6 times
bullet-joined.

Structural fix:
- Add notes?: string[] to UsageReport (interface + both schema
  copies: usage.ts and auth-broker/wire-schemas.ts) so the field
  survives the broker client's "+": "reject" deserialization gate.
- Move opencode-go's disclaimer from per-limit notes to
  provider-level notes.

Defensive fix:
- Dedup identical per-limit notes in the TUI aggregate renderer
  (command-controller.ts) via [...new Set(...)].
- Render provider-level notes once above per-account sections in
  all three rendering paths: TUI (command-controller), CLI
  (usage-cli), and ACP (usage-report helper).

Regression tests:
- usage-cli.test.ts: provider-level notes render once, not
  duplicated per account or limit; positioned above per-account rows.
- usage-report-notes-schema.test.ts: wire-schema round-trip proving
  notes survives usageResponseSchema validation.

Fixes #3268

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -1583,6 +1583,13 @@ function renderUsageReports(
 			lines.push(`  ${uiTheme.fg("accent", "in use by this session:")} ${activeAccountLabel}`);
 		}
 
+		// Provider-wide disclaimers (e.g. "OMP-observed spend only") render once
+		// above the per-account sections instead of duplicating onto every limit.
+		const providerNotes = [...new Set(providerReports.flatMap(report => report.notes ?? []))];
+		if (providerNotes.length > 0) {
+			lines.push(`  ${uiTheme.fg("dim", providerNotes.join(" • "))}`.trimEnd());
+		}
+
 		const resetAccountLines: string[] = [];
 		for (const report of providerReports) {
 			const count = report.resetCredits?.availableCount ?? 0;
@@ -1651,7 +1658,7 @@ function renderUsageReports(
 			if (resetText) {
 				lines.push(`  ${uiTheme.fg("dim", resetText)}`.trimEnd());
 			}
-			const notes = sortedLimits.flatMap(limit => limit.notes ?? []);
+			const notes = [...new Set(sortedLimits.flatMap(limit => limit.notes ?? []))];
 			if (notes.length > 0) {
 				lines.push(`  ${uiTheme.fg("dim", notes.join(" • "))}`.trimEnd());
 			}