Both pollers wait about ten minutes for the agent's token, then exit 0.
Under Restart=on-failure that exit is final, and nothing started them
again, so a token minted or placed after the window left the agent
without notifications until its container restarted.
Add a path unit per poller with PathChanged on the token file(s) the
poller reads, the shape forge-avatar-sync already uses. A path unit
starts its service only when it is not running, so a poller that found
its token is untouched. The github path unit is gated on
github.enable like its service.
Container-side: it ships with the agent's next rebuild, and an agent on
an older rev keeps the old behaviour.
Closes#6179
Every docs directory moves under 1-getting-started, 2-handbook,
4-implementation or 5-project; the options reference (section 3) comes from
the website and has no directory here. trust-boundary stays whole under the
handbook for now. web-ui, swarm and tools split between handbook and
implementation, and the command-line references move to
2-handbook/reference. Links, path references in code and nix, and the docs
index follow the moves; no page content changes.
