feat(plugins): fold first-party plugins in-tree; bundled + external roots

First-party plugins (host_agent, http, snmp, traefik, unifi, docker) are now
tracked under plugins/ and baked into the image, so they version atomically
with core — ending the cross-repo import drift the roundtable->steward rename
exposed. History for these files is preserved in the archived Roundtable-plugins
repo.

Plugin discovery becomes multi-root: PLUGIN_DIR (single) -> PLUGIN_DIRS
(bundled first, then external) + PLUGIN_INSTALL_DIR. Bundled ships in the image;
third-party plugins still mount at runtime into the external root
(STEWARD_PLUGIN_DIR, default /data/plugins) and downloads/installs land there.
Bundled shadows external on a name collision.

- config.py: load_bootstrap returns plugin_dirs + plugin_install_dir
- app.py: iterate PLUGIN_DIRS at the migration + load sites
- migration_runner.py: discover_all_in() unions every plugin root
- plugin_manager.py: resolve_plugin_path() (pure, first-root-wins); load /
  install / hot-reload span all roots; installs target the external root
- settings/routes.py: _discover_plugins scans all roots, dedup bundled-first
- Dockerfile: COPY plugins/ ; docker-compose: drop host bind, document external
- tests/test_plugin_dirs.py: resolution, multi-root discovery, bootstrap split

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/snmp/templates/snmp/index.html

@@ -0,0 +1,57 @@
+{# plugins/snmp/templates/snmp/index.html #}
+{% extends "base.html" %}
+{% block title %}SNMP — Fabled Scryer{% endblock %}
+{% block content %}
+<div style="display:flex;align-items:center;gap:1rem;margin-bottom:1.5rem;">
+  <h1 class="page-title" style="margin:0;">SNMP Devices</h1>
+  <span style="font-size:0.8rem;color:var(--text-dim);">{{ devices|length }} device(s) configured</span>
+</div>
+
+{% if not devices %}
+<div class="card" style="color:var(--text-muted);text-align:center;padding:2rem;">
+  No SNMP devices configured. Add devices to <code>plugin.yaml</code>.
+</div>
+{% else %}
+
+{% for device in devices %}
+<div class="card" style="margin-bottom:1rem;">
+  <div style="display:flex;align-items:center;gap:1rem;margin-bottom:1rem;">
+    <h2 style="margin:0;font-size:1rem;font-weight:600;">{{ device.name }}</h2>
+    <span style="font-size:0.78rem;color:var(--text-dim);">{{ device.host }}</span>
+    {% if device.readings %}
+    <span style="font-size:0.75rem;color:var(--green);margin-left:auto;">&#9679; reachable</span>
+    {% else %}
+    <span style="font-size:0.75rem;color:var(--text-dim);margin-left:auto;">&#9675; no data yet</span>
+    {% endif %}
+    <a href="/plugins/snmp/device/{{ device.name }}" class="btn btn-ghost" style="font-size:0.78rem;padding:0.2rem 0.6rem;">History</a>
+  </div>
+
+  {% if device.readings %}
+  <div style="display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:0.75rem;">
+    {% for oid_cfg in device.oids %}
+    {% set label = oid_cfg.label if oid_cfg.label else oid_cfg.oid %}
+    {% set val = device.readings.get(label) %}
+    <div style="background:var(--bg-alt);border-radius:6px;padding:0.6rem 0.9rem;">
+      <div style="font-size:0.72rem;color:var(--text-dim);margin-bottom:0.2rem;font-family:monospace;">{{ label }}</div>
+      {% if val is not none %}
+      <div style="font-size:1.1rem;font-weight:600;font-variant-numeric:tabular-nums;">
+        {% if val >= 1000000 %}{{ "%.2f"|format(val / 1000000) }}<span style="font-size:0.75rem;color:var(--text-muted);">M</span>
+        {% elif val >= 1000 %}{{ "%.1f"|format(val / 1000) }}<span style="font-size:0.75rem;color:var(--text-muted);">K</span>
+        {% else %}{{ "%.4g"|format(val) }}{% endif %}
+      </div>
+      {% else %}
+      <div style="font-size:0.85rem;color:var(--text-dim);">—</div>
+      {% endif %}
+    </div>
+    {% endfor %}
+  </div>
+  {% else %}
+  <p style="font-size:0.85rem;color:var(--text-muted);margin:0;">
+    No readings yet — waiting for next poll cycle.
+  </p>
+  {% endif %}
+</div>
+{% endfor %}
+
+{% endif %}
+{% endblock %}