Extracts long-form sections to docs/ to reduce README from 784 to
~400 lines before introducing trilingual translation. Also fixes
three positioning issues flagged in the v0.6.0 post-release review.

Extractions (content preserved in docs/, replaced in README with
intent + link):
- SSH Notifications setup/manual config/nonce registration/
  troubleshooting -> docs/notifications.md (new, 136 lines).
  README section shrinks from ~120 lines to ~25.
- Full command reference (all flags, Windows workflow, environment
  variables) -> docs/commands.md (new, 69 lines). README section
  shrinks to the 10 most-used commands.
- Four troubleshooting entries already duplicated in
  docs/troubleshooting.md (SSH ControlMaster, stale sshd, token
  expired, launchd pngpaste) -> deleted from README.
- "Setup fails: killed during re-deployment" -> appended to
  docs/troubleshooting.md (was README-only).

Content fixes (no extraction, just correctness):
- Headline: clarified that notifications apply to Claude Code and
  Codex CLI, not opencode (which is listed but notifications are
  ⚠️ in the Supported Remote CLIs table — avoid headline overclaim).
- Solution data flow: added opencode row (previously only Claude
  Code and Codex CLI were shown, but opencode is a supported
  remote CLI since v0.6.0).
- Windows Quick Start: added experimental callout with pointer to
  open #30 (clipboard persistence hardening) so users don't assume
  v0.6.0 fixed both parts of #27.
- Configuration table: collapsed duplicate "top + details" into a
  single table with a link to docs/commands.md.

Out of scope (future PRs):
- Any translation work.
- i18n scaffold (README.zh-CN.md, README.ja.md, docs/i18n/).
- Removing more low-frequency troubleshooting entries — pending
  evidence from post-release issue frequency.

Ref: i18n prep sequence (step 1 of 5).

MEDIUM (README:228) — `setup` vs `connect` table used
`cc-clip setup myserver [--codex]` as if the brackets were literal
shell syntax. First-time users copy-pasting it would hit
`zsh: no matches found: [--codex]`. Split the column into two
explicit commands (Claude-only / Claude + Codex), each a
ready-to-paste string. Reverted the bracket-annotation anti-pattern
at the same time.

MEDIUM (README:247) — the Mermaid diagram and numbered path list
under "How It Works" omitted opencode, even though the Solution
data-flow block at README:59 and the Supported Remote CLIs table
both call it out. This is exactly the canonical-source
inconsistency that would get multiplied into the ZH and JA
translations, so fix it before the i18n scaffold:

- Added an `M["opencode"]` node to the Mermaid graph routed through
  the same `xclip / wl-paste shim` edge as Claude Code (shim is now
  renamed in the diagram to reflect both binaries it intercepts).
- Inserted a new numbered path 2 describing the opencode flow
  explicitly as "same shim as the Claude Code path" so readers
  don't have to infer it from the diagram.
- Expanded the Codex path 4 annotation with the `arboard` reason
  for why that path needs its own Xvfb/x11-bridge instead of the
  shim.

No LOW items fixed in this commit:
- LOW on `--from-codex-stdin` not appearing in `cc-clip --help` is a
  CLI gap, not a doc gap (the flag does work). Tracking separately.
- LOW on "slim to 400" framing applied to chat context, not the PR
  body (which already reads "-20% from 784 to 631").

Review flagged that the "two sudo-requiring contents" (Xvfb install
on Debian/Ubuntu via apt, on RHEL/Fedora via dnf) were mentioned
only in Step 3's parenthetical and in the Requirements section —
after users had already decided to add --codex. Users on servers
without passwordless sudo would walk through the entire setup flow
before discovering they need to open a ticket with IT.

Fixes:

1. Decision table now has a fourth column "Remote sudo needed?"
   with check/cross per workflow. Only the Claude + Codex row needs
   sudo; Claude-only, opencode, and Windows workflows do not.

2. A new callout directly under the table explains the sudo
   prerequisite, the two package-manager commands, the
   abort-and-retry flow, and the fallback (skip --codex if neither
   passwordless sudo nor manual install is possible).

3. Step 3 bullet 1 (Xvfb) promotes the sudo requirement from a
   parenthetical to a bolded "Requires sudo" statement so readers
   skimming the "what --codex adds" section also see it.

Semantics-preserving: no new prerequisites invented, just made
existing ones visible at the decision point rather than after
commitment.