docs(cli): the node ladder prefers your own node; document --local and the no-node error

[MichaelTaylor3d]

Documents the behaviour shipping in DIG-Network/digs#37
(dig_ecosystem#2099). Docs and code land together per §4.3 — this is the same unit of work, not a
follow-up.

digs used to default to rpc.dig.net. It now prefers your own node, can be pinned per project,
and refuses to publish through a server you never chose. The docs said none of that.

What changed

docs/digstore/cli/command-reference.md

• The config node.url table gains the --local (per-project), --show, and --unset forms.
• The resolution ladder now names all four tiers precisely — including that the project value sits
  between $DIG_NODE_URL and the machine-wide value, and that dig.local is tried over HTTPS then
  HTTP, with localhost on 9778/$DIG_NODE_PORT.
• States plainly that your own node comes first: rpc.dig.net is an ordinary node that happens to
  be well known, not a privileged one (dig_ecosystem#1997).
• New "Setting a node per project" — including why a repo-carried node.url is not honoured
  until you approve it: .dig/node.toml arrives with a cloned repository, and digs signs every
  request to a node with your identity key. Explains that approving one project does not approve
  another, that an edited value re-asks, and that a non-interactive run ignores it.
• New "When no local node is running" — reading still works and says so; publishing stops with
  NO_LOCAL_NODE (exit 19), with the real commands (dig-node status, dig-node start) and where
  to install.

docs/rpc/dig-remote.md — the same ladder, corrected in the dig:// host-resolution section,
plus that an unconfigured origin now means your node.

docs/run-a-node/point-a-consumer.md — one line aligned with the above.

Accuracy

Written against the shipped behaviour and the installed binary rather than from the design. Every
command and URL the pages tell a stuck user to run was checked, with a control so the check could
fail:

https://dig.net/install.sh              200
https://dig.net/install.ps1             200
https://docs.dig.net/docs/run-a-node    200
https://docs.dig.net/docs/<bogus>       404   <- control
dig-node status / dig-node start        both exist as subcommands

Per §4.3 these pages stay self-contained: no reference to SPEC.md, SYSTEM.md, or issue numbers —
the reasoning is stated directly, in the user's terms.

Version

0.11.1 → 0.12.0 — minor: new documented capability.