fix(orchestrator): S1 fit, rename once, Deutschlandfunk e2e, squelch, tree cause

Requirement 001 phase 6, S1:

- Fit: Agents and Artifacts in a graph view fill the window from 861 px
  up (body.fit flex column); the e2e walk probes #agents/orbit at every
  width for a page no taller than the window.
- Rename once: a session seen under two names by one source (two claims)
  flipped its name on every state build, so the Stream logged a rename
  each poll. Names.observe keeps only the newest sighting per session
  and source, and the timeline emits each (session, before, after) pair
  once.
- Deutschlandfunk: root cause was the signed media-src, which never
  listed the redirect target f111.rndfnk.com that st01.sslstream.dlf.de
  answers with (fixed in ba97f7c). The e2e now replays that chain, a
  302 from one https origin to a second, in Chromium and Firefox, with
  self-signed throwaway certificates the drivers accept.
- Squelch: a settings slider 0..1 scales every tone; at 0 no beep plays,
  music on or off (Voice.beep skips a silent tone). Stored settings
  without the key load with 1.0.
- Tree: the missing tree file error names `pkgmgr branch tree` and the
  release and install step that makes the timer write it.

Evidence: make test 655 OK, ruff and markdownlint clean
(/tmp/s1-make-test-1.log); e2e 17 OK, none skipped (/tmp/s1-e2e-3.log);
MEDUSA 14 files, 0 findings.

🎯 Fix: 94 %
💥 Break: 4 %
💸 Cost: 100 %
⏱️ Time: –
🛡️ Security: 100 %
🏆 Score: 90
🚦 Gate: ✅ 90/5, cost and time <= 100, security 100 %

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

orchestrator/kvb_orchestrator/tree.py

@@ -191,7 +191,10 @@ class Tree:
             try:
                 info = self.file.stat()
             except OSError as error:
-                return {"repos": [], "scanned": None, "error": f"no pkgmgr tree file at {self.file}: {error.strerror}"}
+                return {"repos": [], "scanned": None, "error": (
+                    f"no pkgmgr tree file at {self.file}: {error.strerror}. The tree timer runs `pkgmgr branch tree`, which the installed pkgmgr "
+                    "lacks until a release ships it: release pkgmgr and install it, then the timer writes the file within a minute."
+                )}
             stamp = (info.st_mtime_ns, info.st_size)
             if self.cached is None or stamp != self.stamp:
                 self.cached, self.stamp = read_tree(self.file), stamp