feat(status-bar): add /battery toggle for a color-coded battery read-out

[OutThisLife]

Summary

Adds an opt-in battery indicator to the CLI and TUI status bars, rendered as the first element and color-coded by charge — the way many shell prompts show it. Off by default; a no-op on machines without a battery (desktops/servers/VMs).

• ⚡ 82% while charging, 🔋 82% on battery.
• Colors: green (>50% or charging) → yellow (≤50%) → orange (≤20%) → red (≤10%), reusing the existing status-bar style classes / theme colors.

What's in it

• agent/battery.py — a small shared, psutil-backed reader (psutil is already a dependency). Memoises the reading for a few seconds so the status bar can poll it on every repaint cheaply, buckets the level into a color category, and formats a compact label. Every failure path degrades to "unavailable" and simply renders nothing.
• CLI — /battery [on|off|status] toggles the read-out and persists to display.battery (survives restarts). Prepended ahead of the ⚕ marker in every status-bar width tier (both the fragment and plain-text renderers).
• TUI — /battery slash command, display.battery config sync, a system.battery JSON-RPC method that returns the reading, a poller that runs only while the indicator is enabled, and a pinned first segment in StatusRule (width-budgeted so it never crushes model/context).
• Docs entry in website/docs/reference/slash-commands.md.

Footprint

No new core model tool and no new .env var — this is a display setting in config.yaml (display.battery, default false) toggled by a CLI-only slash command, consistent with /statusbar, show_cost, etc.

Test plan

• tests/agent/test_battery.py — reader (no psutil / no battery / clamp / cache) + category thresholds + label/glyph.
• tests/test_tui_gateway_server.py — system.battery (reading + fail-open) and config.set battery (toggle + explicit off).
• ui-tui vitest — StatusRule battery rendering/coloring/omission + toBatteryInfo coercion.
• npm run typecheck + eslint clean on changed TUI files.
• Existing CLI status-bar and command-registry suites still green.
• Manual: /battery on on a laptop (charging + on battery), and confirm it's a no-op on a desktop.

[github-actions]

૮ >ﻌ< ა ci review

_{running on 3c2903a}

looks good to me!

[Copilot]

Pull request overview

This PR adds an opt-in, color-coded battery indicator to Hermes’ CLI and TUI status bars, backed by a shared psutil reader and surfaced via a new /battery toggle plus a TUI JSON-RPC endpoint.

Changes:

• Introduces agent/battery.py to read/cache battery state and derive a color category + compact label.
• Wires the battery segment into the CLI status bar (text + fragments) and adds /battery [on|off|status] with persistence via display.battery.
• Adds TUI support via system.battery, a polling hook, status-bar rendering updates, and accompanying Python/TS tests + docs.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
agent/battery.py	New shared battery reader/category/formatter with short TTL caching.
cli.py	Adds /battery handler, persists display.battery, and prepends battery segment in status bar rendering.
hermes_cli/commands.py	Registers the new CLI-only /battery slash command.
hermes_cli/config.py	Adds display.battery default config key (off by default).
tui_gateway/server.py	Adds system.battery RPC and supports config.set for battery persistence.
tests/agent/test_battery.py	Unit tests for battery reading/clamping/caching, category thresholds, and formatting.
tests/test_tui_gateway_server.py	Tests system.battery fail-open behavior and config.set battery persistence.
ui-tui/src/gatewayTypes.ts	Adds display.battery typing and SystemBatteryResponse RPC type.
ui-tui/src/app/interfaces.ts	Introduces BatteryInfo / BatteryCategory and stores them in UiState.
ui-tui/src/app/uiStore.ts	Initializes battery UI state (battery, batteryStatus).
ui-tui/src/app/useConfigSync.ts	Syncs display.battery from gateway config into UI state.
ui-tui/src/app/useBatteryPoll.ts	New polling hook + coercion helper for system.battery payloads.
ui-tui/src/app/useMainApp.ts	Enables the battery poller alongside other config-driven hooks.
ui-tui/src/app/slash/commands/core.ts	Adds TUI /battery command to toggle the indicator and persist via config.set.
ui-tui/src/components/appLayout.tsx	Plumbs battery state into StatusRule.
ui-tui/src/components/appChrome.tsx	Renders a pinned first battery segment with category-based coloring.
ui-tui/src/__tests__/useBatteryPoll.test.ts	Tests payload coercion/clamping and category normalization.
ui-tui/src/__tests__/appChromeStatusRule.test.tsx	Verifies StatusRule battery segment rendering/coloring/omission behavior.
website/docs/reference/slash-commands.md	Documents /battery and marks it CLI-only in the notes section.

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