docs+install: post-rename docs polish, install script, d2 architecture diagram (#26)

* docs: add sanderling bird artwork to README and docs index

* chore: add one-line install script for macOS and Linux

Detects os/arch, resolves latest (or pre-)release, verifies sha256,
and installs the binary into $HOME/.sanderling/bin.

* docs: use the one-line installer in getting-started

Replaces the broken `<version>` placeholder snippets with the
install.sh one-liner.

* docs: drop filler line under the install one-liner

* docs: rename index heading to Sanderling Manual

* docs(style): adopt JetBrains Mono and uppercase brand mark

* docs(getting-started): use justfile flow for folio sample

* docs(writing-specs): drop 'coming soon' notes for eventually and implies

* docs(inspect): rewrite layout for tabbed state panels and metrics chart

* docs(inspect): add UI screenshot

* docs: add Inspect to sidebar and index

* docs: restore mermaid bootstrap script in page template

* docs(style): constrain article images to content width

* docs(inspect): drop layout prose, keep what the screenshot doesn't show

* docs(architecture): add d2 source for architecture diagram

Replaces the in-page mermaid block with a d2-rendered SVG. Generated
outputs (svg/png) stay out of git; only the .d2 source is checked in.

* build(docs): render d2 diagrams into build/site/_assets/diagrams

* docs(architecture): swap mermaid block for rendered d2 svg

* ci(docs): install d2 before building the site

* docs(architecture): tighten layout and reroute label-crossing edges

Flip device/sidecar order so trace writer drops cleanly to runs/
without cutting through the JVM cell, right-align the inspect row
via a pad column, and tune grid gaps to keep gRPC and Unix socket
labels off the SANDERLING boundary.

install.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+#
+# Installs the sanderling CLI on macOS or Linux.
+#
+# Usage:
+#   curl -fsSL https://raw.githubusercontent.com/priyanshujain/sanderling/master/install.sh | bash
+#
+# Environment:
+#   SANDERLING_VERSION  Tag to install (default: latest release)
+#   SANDERLING_INSTALL  Install prefix (default: $HOME/.sanderling); binary lands in $prefix/bin
+
+set -euo pipefail
+
+REPO="priyanshujain/sanderling"
+PREFIX="${SANDERLING_INSTALL:-$HOME/.sanderling}"
+BIN_DIR="$PREFIX/bin"
+
+os="$(uname -s)"
+arch="$(uname -m)"
+case "$os" in
+  Darwin) os=darwin ;;
+  Linux)  os=linux ;;
+  *) echo "sanderling: unsupported OS '$os' (need Darwin or Linux)" >&2; exit 1 ;;
+esac
+case "$arch" in
+  x86_64|amd64)  arch=amd64 ;;
+  arm64|aarch64) arch=arm64 ;;
+  *) echo "sanderling: unsupported arch '$arch' (need amd64 or arm64)" >&2; exit 1 ;;
+esac
+
+version="${SANDERLING_VERSION:-}"
+if [ -z "$version" ]; then
+  # /releases/latest skips pre-releases; fall back to /releases for the
+  # newest tag of any kind so alphas remain installable.
+  version="$(curl -fsSL "https://api.github.com/repos/$REPO/releases/latest" 2>/dev/null \
+    | awk -F'"' '/"tag_name":/ {print $4; exit}')"
+fi
+if [ -z "$version" ]; then
+  version="$(curl -fsSL "https://api.github.com/repos/$REPO/releases?per_page=1" \
+    | awk -F'"' '/"tag_name":/ {print $4; exit}')"
+fi
+if [ -z "$version" ]; then
+  echo "sanderling: could not resolve a release tag" >&2; exit 1
+fi
+
+stripped="${version#v}"
+tarball="sanderling_${stripped}_${os}_${arch}.tar.gz"
+base="https://github.com/$REPO/releases/download/${version}"
+
+tmp="$(mktemp -d)"
+trap 'rm -rf "$tmp"' EXIT
+
+echo "sanderling: downloading $tarball ($version)"
+curl -fsSL -o "$tmp/$tarball"      "$base/$tarball"
+curl -fsSL -o "$tmp/checksums.txt" "$base/checksums.txt"
+
+if command -v sha256sum >/dev/null 2>&1; then
+  ( cd "$tmp" && grep "  $tarball\$" checksums.txt | sha256sum -c - >/dev/null )
+elif command -v shasum >/dev/null 2>&1; then
+  ( cd "$tmp" && grep "  $tarball\$" checksums.txt | shasum -a 256 -c - >/dev/null )
+else
+  echo "sanderling: no sha256 tool available, skipping checksum verification" >&2
+fi
+
+tar -xzf "$tmp/$tarball" -C "$tmp"
+mkdir -p "$BIN_DIR"
+mv "$tmp/sanderling" "$BIN_DIR/sanderling"
+chmod +x "$BIN_DIR/sanderling"
+
+echo "sanderling: installed $version to $BIN_DIR/sanderling"
+
+case ":$PATH:" in
+  *":$BIN_DIR:"*) ;;
+  *) echo "sanderling: add $BIN_DIR to PATH, e.g. 'export PATH=\"$BIN_DIR:\$PATH\"'" ;;
+esac