fix(git,macos,runs): close the review findings on #22, #34 and #38

- validateRemoteUrl checks the literal scheme prefix git will receive and
  refuses %/backslash in the authority (WHATWG normalises https:/host and
  percent-escapes that git reads differently); route test for EBADURL.
- Parent-session scrub also drops AI_AGENT, and GIT_EDITOR when it is
  Claude Code's `true`.
- canonicalCwd resolves a not-yet-existing path through its deepest
  existing ancestor, so a symlinked parent still yields one lane.
- Note the clock-step ceiling on liveServers' boot-time filter.
- Docs/header wording: the Active runs count is lane-scoped.

server/__tests__/git-diff-ops.test.js

@@ -735,6 +735,15 @@ describe("an unborn repo and `publish`", () => {
       "https://host/r .git",
       "https://host/r.git\n",
       "ssh://-oProxyCommand=x/r.git",
+      // WHATWG parses these as https://host/x, but git sees no "://" and reads
+      // them as scp-like ssh to a host named "https" — the checked string and
+      // the used string must be the same string.
+      "https:/host/r.git",
+      "https:host/r.git",
+      "https:\\\\host\\r.git",
+      // Percent-encoded userinfo/host that git decodes into a leading "-".
+      "ssh://%2DoProxyCommand=x@host/r.git",
+      "ssh://git@%2Dhost/r.git",
       "-git@host:r.git",
       "",
       42,