feat(client): add plans & quota sidebar panel, real-time session cost readout, and price table remote

[xer-on]

Summary

This PR introduces three major UI and client-side capability upgrades for the Command Code provider plugin:

1. Plans & Quota Dashboard & Sidebar Footer Card: A dedicated footer action in the sidebar (sidebar.footer.action) that reveals current plan details, 5-hour and weekly quota depletion bars, monthly credit balances (limit - remaining), and token statistics, which opens a full dashboard in the center workspace column (main slot).
2. In-Composer Real-time Session Cost Readout: An unobtrusive cost indicator injected into the composer dock (conversation.composer.dock) that decorates the official token-usage pill with session cost estimates in USD and adds per-token cost breakdown rows into the usage dialog.
3. Vendored Model Pricing Catalog & Remote Contract: A new Host-side price table (commandcode/prices) exposing official per-token rates (input, output, cache-read, cache-write) in USD per million tokens, factoring in weekday peak/off-peak pricing schedules.

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Key Features & Changes

1. Plans & Quota Sidebar Card & Center Dashboard

• Sidebar Footer Card: Registers under sidebar.footer.action (order 1), placing it immediately above the Settings seat. Shows live status and opens the dashboard on click via ctx.layout.selectPanel().
• Center Dashboard Panel: Registers in the layout's main slot as commandcode-panel. Renders:
  • Account plan badge and billing cycle end dates.
  • 5-hour and weekly quota usage progress bars with automatic reset timers.
  • Monthly credit consumption using the official CLI derivation formula (limit - remaining).
  • Purchased vs. free credit tile breakdown.
• Throttled Auto-Refresh: Background refresher keeps quota and token statistics current without overwhelming the API gateway.
• Pure / React-Free Controller: Implemented in src/client/panel.ts so view-model logic and formatting can be tested without a DOM.

2. In-Composer Session Cost & Dialog Breakdown

• Non-Destructive Pill Injection: Rather than replacing the stock stats dock cell (which would break upstream i18n and formatting), src/client/session-cost-display.ts decorates the existing token-usage button pill with dollar figures (e.g. · $0.02).
• Usage Dialog Breakdown: Uses a lightweight MutationObserver on document.body to match and inject cost lines directly into the token details dialog (Uncached input, Completion, Cache read, Cache write).
• Strict Guardrails:
  • Only computes cost for sessions routed through the commandcode provider.
  • Never fabricates unpriced cache-write rates; leaves unpriced rates clearly indicated.
  • Renders invisible if unpriceable or unknown, avoiding misleading zero-dollar figures.

3. Model Pricing Remote (commandcode/prices)

• Vendored Pricing Data: src/model-prices.ts defines official pricing rows matching Command Code docs in USD / 1M tokens.
• Typert Gateway Contract: Declares the commandcode/prices endpoint in src/usage-wire.ts and wires it in src/usage-remote.ts.
• Peak / Off-Peak Calculation: Accurately determines weekday peak windows and applies peak-rate overrides for time-of-day models.

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Architectural Notes

• Clean Decoupling: All new controllers (src/client/panel.ts, src/client/session-cost.ts, src/client/prices.ts) are decoupled from React and JSX.
• Resilient Registration: Slot injections (main, sidebar.footer.action, conversation.composer.dock) are wrapped in defensive guards so individual surface failures cannot crash the entire plugin fiber.

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Verification

• Verified snapshot store subscription and disposal lifecycle.
• Tested quota progress bar and depletion percentage calculations.
• Tested session cost calculator across free models, flat-rate models, and time-of-day peak models.