feat: cross-project usage browser command with multi-panel navigation

[jonasotoaguilar]

Affected Area

Frontend / UI

Problem Statement

TokenMeter currently renders usage only for the active project/session in the current OpenCode directory. There is no in-TUI way to inspect lifetime usage across other known projects and their historical sessions without manually opening OpenCode in each project directory.

Users working across multiple projects need a read-only browser to answer: which projects have the most lifetime spend, which sessions within a project are heaviest, and how provider/model breakdown looks per project/session.

Proposed Solution

Add a native plugin command and palette entry (registered via the supported keymap palette command mechanism, namespace: "palette" / category: "TokenMeter") that opens a cross-project usage browser.

Navigation (multi-panel):

• Projects → list all known projects with lifetime totals.
• Project detail → selected project's aggregate and its session list.
• Sessions → all sessions for that project.
• Session detail → single session's totals and provider/model breakdown.

Data shown per row (read-only): lifetime token and cost totals, active period, last activity (updatedAt/createdAt semantics), and provider/model breakdown where available. All totals reuse the canonical input + output + reasoning + cache.read + cache.write spend model already used for Project/Session (context).

Ordering and pinning: the currently open project/session (if in the known set) is pinned first and visually separated; remaining entries are sorted by recent activity descending.

Scope constraints:

• Read-only: no data editing/deletion, no budgets, no session mutation.
• Reuses the existing Project aggregation (live session.list + persisted deleted-session aggregate) and session store; introduces no second representation of usage truth.
• UI inspiration may reference multi-panel navigation patterns, but the implementation must remain terminal-compatible and must not depend on Nerd Fonts. Do not embed any private local paths or usernames in the UI or docs.

Alternatives Considered

• Open each project directory manually: requires switching directories and loses cross-project comparison.
• Extend the sidebar to show all projects inline: would crowd the existing Project/Session/Subagents hierarchy and exceed the sidebar's width/height budget.
• Single flat list of sessions: hides the project-level aggregate that users need first.

Additional Context

Follow the existing palette command seam (api.keymap.registerLayer → api.ui.dialog.replace / DialogSelect) used by TokenMeter: Settings and the sidebar width/height conventions. Source of truth for totals must remain the existing aggregation paths; the browser is presentation only.

Systemic bucket: D — feature request.

Duplicate check: searched open/closed issues for browser, cross-project, progressive disclosure, command, settings — no existing issue owns the cross-project browser or multi-panel navigation (closest is #20 progressive disclosure, which is sidebar-only and closed).

Privacy note: examples use <project-name> placeholders; no absolute paths, usernames, or session payloads are embedded.