v0.9.0 — New model support + Codex discovery fixes

• New model support — Claude Fable 5 / Mythos 5, Sonnet 5, Opus 4.8, GPT-5.x Codex (#57)
  • Context window sizing: fable/mythos family recognized as 1M context (previously fell back to 200k, showing the gauge 5× overfull); gpt-* family recognized as 400k as the fallback when Codex doesn't report its own authoritative window. Sonnet 5 / Opus 4.8 already matched the existing family patterns
  • Cost display: per-model-family blended $/M rates (Fable/Mythos $10/$50, Opus $5/$25, Sonnet $3/$15, Haiku $1/$5, GPT-5.x Codex $1.75/$14) replace the single Sonnet-class rate that was applied to every agent. Agents now carry the detected model ID, and the cost pill, summary panel, and per-tool breakdown all use the owning agent's rate
• Codex session discovery fixes — addresses reports of Codex sessions not appearing
  • Windows: workspace/cwd matching is now case-insensitive on win32 (VS Code reports c:\..., Codex writes C:\... — sessions never matched)
  • Large session_meta: the first-line reader now grows up to 1MB instead of a fixed 64KB — newer Codex versions embed full base instructions and AGENTS.md content, which silently broke cwd extraction and skipped the session
  • Silent cwd mismatch: when recent Codex sessions exist but none ran in the current workspace, a warning now says so (the most common cause: launching npx agent-flow-app from a different directory than the Codex session). Warnings are visible without --verbose
• Fix: assistant messages in Codex sessions were labeled "CLAUDE" in the transcript panels and canvas bubbles — the label now follows the session runtime ("CODEX") (#49)