feat(cli): keyed credentials — servers:, the token chain, login/logout (RFC-007 PR 2)

The operator config gains servers: (name -> url; never a token). A remote
command whose URL prefix-matches an operator server resolves its bearer
token through the keyed chain first — OMNIGRAPH_TOKEN_<NAME> env, then the
[<name>] section of ~/.omnigraph/credentials (created 0600 via temp+rename,
#139 finding 7; group/world-readable files refused loudly) — falling
through to the legacy chain unchanged. URL keying makes §D5 rule 3
structural: a token is only ever sent to the server it is keyed to.
Longest-prefix matching with a path-boundary check (http://h:8080 never
matches http://h:8080-evil). Inserting the keyed hop above the legacy chain
is safe by construction — no existing setup can have servers: defined.

omnigraph login <name> stores/rotates one section (token from --token or
one stdin line — the pipe flow keeps secrets out of shell history);
omnigraph logout removes it, idempotently; logging in before declaring the
server warns instead of failing (the gh model).

Coverage: URL-match/no-substring-trap, credentials round-trip preserving
sibling sections, 0600 write + over-permissive refusal, env-name mapping;
the legacy resolve test is now hermetic against a real ~/.omnigraph and
asserts byte-identical legacy behavior with no servers defined; one
spawned-binary e2e walks the whole lifecycle against an authed server:
refusal -> wrong-token login (stdin) -> rotate (--token) -> authorized read
-> env-beats-file -> non-matching-URL negative -> logout revokes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/omnigraph-cli/src/output.rs

@@ -828,3 +828,48 @@ pub(crate) struct QueriesListItem {
 pub(crate) struct QueriesListOutput {
     pub(crate) queries: Vec<QueriesListItem>,
 }
+
+pub(crate) fn finish_login(
+    server: &str,
+    credentials_path: &std::path::Path,
+    declared: bool,
+    json: bool,
+) -> Result<()> {
+    if json {
+        print_json(&serde_json::json!({
+            "server": server,
+            "credentials_path": credentials_path.display().to_string(),
+            "declared": declared,
+        }))?;
+    } else {
+        println!(
+            "stored credential for '{server}' in {}",
+            credentials_path.display()
+        );
+    }
+    if !declared {
+        eprintln!(
+            "note: '{server}' is not declared under servers: in the operator config; the token applies once you add `servers:\n  {server}:\n    url: <server url>` to ~/.omnigraph/config.yaml"
+        );
+    }
+    Ok(())
+}
+
+pub(crate) fn finish_logout(
+    server: &str,
+    credentials_path: &std::path::Path,
+    json: bool,
+) -> Result<()> {
+    if json {
+        print_json(&serde_json::json!({
+            "server": server,
+            "credentials_path": credentials_path.display().to_string(),
+        }))?;
+    } else {
+        println!(
+            "removed credential for '{server}' from {}",
+            credentials_path.display()
+        );
+    }
+    Ok(())
+}