feat(cli): add Session pace and JSON pace output

[kmatsunami]

What

• codexbar usage (text): adds a Pace line under Session, mirroring the GUI's session pace calculation (5-hour window; codex/claude/ollama). Session uses the GUI wording "Projected empty in …"; Weekly keeps "Runs out in …".
• --format json: adds a derived pace object to each provider payload.

JSON shape

pace.primary = session window, pace.secondary = weekly window. A key is emitted only when the corresponding text Pace line would render; nil sub-objects/fields are omitted (consistent with the existing payload style).

"pace": {
  "primary":   { "stage": "...", "deltaPercent": 30, "expectedUsedPercent": 20,
                 "actualUsedPercent": 50, "willLastToReset": false,
                 "etaSeconds": 3600, "summary": "30% in deficit | Expected 20% used | Projected empty in 1h" },
  "secondary": { "...": "...", "summary": "4% in deficit | Expected 4% used | Runs out in 3d" }
}

• deltaPercent = actualUsedPercent − expectedUsedPercent (positive = ahead of pace / deficit; negative = behind / reserve).
• etaSeconds / runOutProbability omitted when nil; summary is the same content as the text Pace line (minus the Pace: label).

Implementation

• Shared computePace + paceSummary helpers in CLIRenderer so text and JSON output stay in sync.
• PaceKind (session = 300 min / weekly = 10080 min) with provider guards matching the GUI's UsagePaceText.sessionPace.
• Additive only — no existing JSON keys changed.

Test

• swift test --filter CLISnapshotTests → 32 passing, including 4 new JSON pace tests and the session-pace text tests; related CLI suites green.
• swiftformat --lint clean.

🤖 Generated with Claude Code

[kmatsunami]

Recreating: this PR's diff was computed against a stale base (fork main was 1278 commits behind upstream). main is now fast-forwarded to upstream tip; reopening so the diff shows only the 4 feature files.