docs: sync STATUS.md with the merged perf epic (#81) and v0.8.0

[Zeus-Deus]

Docs-only follow-up that closes out epic #81's paper trail. All nine sub-issues (#72–#80) merged via PRs #83–#91 (+ the containerized e2e harness in #93); this syncs docs/core/STATUS.md to that reality:

• Adds the epic summary to the unreleased-changes headline ([perf][terminal] Enable the xterm.js WebGL renderer (addon already installed, never loaded) #72 WebGL renderer, [perf][terminal] Apply PTY producer back-pressure on the live terminal path #73 live-path back-pressure, [perf] Move blocking workspace.rs commands off the GTK main thread (async + spawn_blocking) #74/[perf] Move blocking files.rs commands off the GTK main thread (async + spawn_blocking) #79 async workspace.rs/files.rs, [perf][agent-chat] Stream agent-chat events over a Tauri Channel instead of the global event bus #75 per-thread chat Channels, [git] Fetch origin before creating a new workspace branch so it starts from the latest remote #76 fetch-before-branch, [perf][chat] Virtualize the agent-chat message list #77 virtualized transcript, [remote] Headless daemon worktree creation: run setup scripts + fetch-before-branch (desktop parity) #78 daemon provisioning parity, [feature] Optional background rollback checkpoint at agent-run start #80 run-start checkpoints).
• Fixes the stale "backpressure is inert in production today" bullet — issue [perf][terminal] Apply PTY producer back-pressure on the live terminal path #73 wired the live TerminalPane path (write-pump HIGH/LOW watermarks → pause_pty_output/resume_pty_output, in-process flow_paused gate with FLOW_MAX_PARK backstop), which docs/features/terminal.md already documents; STATUS.md now agrees.
• Reframes the OpenCode-sync / favicon-fix / dev-mock trio as shipped in v0.8.0 (the tag exists at the version bump) and dates the epic + daemon-parity paragraphs relative to v0.8.0 instead of v0.7.9.

Epic verification that motivated this (full detail in the closing comment on #81): npm run verify green (cargo check, 1729+ cargo tests, tsc, 1839 vitest), Docker clean-host daemon worktree e2e PASS, and browser e2e of channel streaming, transcript virtualization (484 items → 11–20 DOM rows), checkpoint toggle + restore flow, and the live webgl2 canvas.