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

enclosure/README.md

@@ -73,8 +73,9 @@ accuracy.
 1. **Base:** set the pan servo on its posts, shaft up, and screw it through the tabs. Press the
    bearing into the seat. Feed the USB-C cable in through the slot at the back of the base, up through
    the bearing.
-2. **Turntable:** screw a double-arm horn into the pocket under the plate. Centre the servo (run the
-   software's `turn_head(0, 0)`, or use a servo tester), press the plate's hub into the bearing so the
+2. **Turntable:** screw a double-arm horn into the pocket under the plate. Centre the servo (with a servo
+   tester, or a 1.5 ms pulse on its PWM channel as in "Arrival day" in `CONTEXT.md`; `turn_head(0, 0)`
+   works only once the head node exists and the bridge has `head: true`), press the plate's hub into the bearing so the
    horn meets the spline, and fit the horn's centre screw through the hole in the plate.
 3. **Body onto the plate:** pass the power cable and the pan servo's lead up through the floor hole.
    Then screw the plate on from inside the body with 4 × M3, before the speaker goes in.