Bring every doc up to date, and give the repo a Wi-Fi template that exists

CONTEXT.md had grown by appending and contradicted itself (all four nodes vs six, a retracted CPU
figure, "no calibration", "nobody enrolled", "audio untested as a service", the Wi-Fi-off boot as
not done, a class the tracker replaced). Rewritten as one current-state document organised by
subsystem, with fresh measurements, the owner's decisions, the gotchas, the neck's arrival-day plan
and what is genuinely still open.

README: status, speakers not fitted, new-session note for Hermes, the calibration section (shipped
calibration, coverage hints, outlier dropping, --from-views), running the tests, the docs row.
HANDOFF.md gets a status banner listing where the original brief has drifted. CLAUDE.md starts at
CONTEXT.md. The echo-cancel config no longer talks about a Pi Zero, and the enclosure guide no longer
tells you to centre a servo with a tool that does not exist yet.

pi/network-config.example is a tracked, credentials-free first-boot template: the README pointed at
pi/50-cloud-init.yaml, which is gitignored and so missing from a fresh clone. The dead IdentityCache
(replaced by the tracker) is removed. Docstrings corrected: audio scope publishing, the MCP health
topics, and what the calibration tool does.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AFN8nRRCiDiMN7ChBpHJhs

pi/pipewire/60-echo-cancel.conf.optional

@@ -4,10 +4,12 @@
 #
 # It creates an echo-cancelled mic ("robot_ec_source") and a matching speaker
 # ("robot_ec_sink"). After enabling it, uncomment the pulse.device lines in the
-# Omarchy tunnel config so the tunnels use these nodes instead of the raw ones.
+# Omarchy tunnel config (host/omarchy/50-robot-tunnel.conf) so the tunnels use these nodes instead of the
+# raw ones.
 #
-# WebRTC echo cancellation costs some CPU; a Pi Zero 2 W manages it at speech rates,
-# but check `top` afterwards.
+# UNTESTED: it only matters once the speakers are fitted (the robot has none yet). WebRTC echo
+# cancellation costs some CPU, and the Pi 4 already runs the whole robot with about 40% of the machine
+# idle; check `top` and `robot://status` (temperature) after enabling it.
 
 context.modules = [
     {   name = libpipewire-module-echo-cancel