v1.8.6: adopt pi 0.84.3 + mempalace 3.8.0, close the v1.8.5 doc/observability gaps

Three coupled pieces of work, all of which ride on the base rebuild that the
mempalace bump forces anyway.

DRIFT ADOPTED
- pi 0.84.2 -> 0.84.3. Its release notes carry a "Breaking Changes" line
  (GoogleThinkingLevel -> GoogleApiThinkingLevel). Audited before adopting:
  zero references across all four vendored companions (pi-fork,
  pi-observational-memory, pi-atelier, pi-studio), so it is inert for us. The
  reason to adopt is two skill-discovery fixes that land directly on v1.8.5's
  vendored-skill work: nested Markdown skills inside grouping directories were
  not discovered, and root README.md/AGENTS.md in skill dirs were reported as
  broken skills.
- mempalace core 3.7.1 -> 3.8.0. Additive/reliability only. Its sync fix
  (#2320/#2322) stops sync --apply deleting drawers whose source_file was
  unreachable *at that moment* -- which does NOT relax the standing landmine
  against sync on the shared palace, because that landmine is about paths
  permanently absent from whichever host runs the sync. Different failure
  shape; the caution stands.

DOCS -- three defects, one of them public
- DOCKER_HUB.md advertised "neovim (LazyVim defaults)". Nothing in the image
  installs LazyVim; the only nvim config is a 19-line sysinit.vim. CI PATCHes
  this file into the Docker Hub description on every release, so this was a
  false claim published to the world. Removed.
- agent-browser + Playwright + Chromium is the single largest addition in the
  image (~625 MB) and had zero mentions in README, DOCKER_HUB or THIRD_PARTY --
  it was documented only to agents, in the AGENTS.md managed block. Now
  documented to humans, including the Chromium licence dimension.
- typst and socat appeared in README prose but not in the "What's inside"
  inventory. Added.

OBSERVABILITY -- the three gaps v1.8.5 listed as still open
- build-manifest.json now records mempalace core, read from the live binary
  (ground truth, not the build ARG). Placed as a sibling of pi_version rather
  than inside components{}, because pi-devbox-version renders that map through
  [0:12] and would truncate a version string.
- smoke asserts the pi-observational-memory clone actually CONTAINS the ce9fc98
  auth fix, pinned to src/runtime.ts. Deliberately not a repo-wide grep: two of
  the three markers also live under tests/, so the repo-wide form stays green
  with the fix site reverted. That is the third false-green of this exact family
  in this repo (canary phrase in both snapshots; reconciler fixture using a
  non-owned name; now this) -- pin containment checks to the fix site.
- smoke asserts the feeder's pi@<device> agent default behaviourally. The
  earlier audit concluded this needed a --print-config added upstream; it does
  not. AGENT is assigned before arg parsing, so `bash -x mempalace-pi-session
  --help` observes the real resolution with no toolkit change. Two-sided:
  device set => pi@<device>, unset => must not be pi@*.
- pi-devbox-version now prints a palace: line with the same live-vs-baked drift
  detection pi already had. This matters more than it looks: mempalace is the
  one component that is both client (here) and server (synlig), so skew between
  them is a real failure mode. Degrades quietly on pre-v1.8.6 images.

Deferred deliberately: a native arm64 act_runner on tor-ms22 (the current
runner is on synlig, x86_64, so every arm64 layer ships QEMU-emulated).
Analysis and caveats filed to the palace rather than actioned here.

README.md

@@ -70,9 +70,27 @@ so `TERM=xterm-kitty` is understood. Override either in your own
 ### Document and image tooling
 
 - `pandoc` — universal Markdown↔HTML/Org/RST/etc. converter
+- `typst` — markup-based typesetting, wired up as pandoc's `--pdf-engine` (see
+  [Generating a PDF with pandoc + typst](#generating-a-pdf-with-pandoc--typst))
 - `graphviz` — `dot` rendering for diagram pipelines
 - `imagemagick` — image conversion / resizing (invoked as `magick`)
 
+### Browser automation
+
+- `agent-browser` — CLI for driving a real headless browser: open pages,
+  click/fill/`eval`, snapshot the DOM, take screenshots. Useful whenever a task
+  involves a web UI or verifying how a page actually renders (live DOM, WebGL,
+  layout, popup positioning) instead of guessing from source.
+- `playwright` + a pre-installed headless **Chromium** back it.
+  `AGENT_BROWSER_EXECUTABLE_PATH` is preset to the baked browser via a stable
+  `/usr/local/bin/agent-chrome` symlink (insulated from Playwright's
+  per-version/arch install directory), so `agent-browser open <url>` works
+  out of the box with no setup. Run `agent-browser skills get core --full`
+  for the command set and workflow patterns.
+- `socat` — TCP bridge used by `studio-expose` to reach pi-studio's
+  loopback-bound server from outside the container (see
+  [Using pi-studio](#using-pi-studio--studio-variant))
+
 ### Language toolchains
 
 - `python3` + `python3-venv` + `python3-pip` (system Python)
@@ -787,8 +805,9 @@ docker inspect --format '{{json .Config.Labels}}' joakimp/pi-devbox:latest | jq
 `org.opencontainers.image.{version,revision,created}` plus
 `se.jordbo.pi-devbox.*-ref` record the intended pi version and companion
 refs. The on-disk `/etc/pi-devbox/build-manifest.json` records **ground
-truth** — the actual checked-out commit of each `/opt` clone and the live
-`pi --version` — so a tag is reconstructable after CI logs rotate:
+truth** — the actual checked-out commit of each `/opt` clone, the live
+`pi --version`, and (from v1.8.6) the live `mempalace --version` of the
+installed palace core — so a tag is reconstructable after CI logs rotate:
 
 ```bash
 docker run --rm --entrypoint= joakimp/pi-devbox:latest cat /etc/pi-devbox/build-manifest.json