feat(templates): hackernews-digest template + dogfooding test harness

First pass of the dogfooding-templates initiative. Each pre-release cycle
ships one new official `.scarftemplate` and uses installing/exercising
that template as the regression test. v1 lands the harness scaffolding
plus the first template under it.

- HackerNews Daily Digest template (`templates/awizemann/hackernews-digest/`):
  config-driven (min_score / max_items / topics) cron-only template.
  No secrets — keeps the harness minimal until the fake-Keychain shim
  lands. Bundle validates against `tools/build-catalog.py`; entry added
  to `templates/catalog.json`.
- `SCARF_HERMES_HOME` env-var override at `HermesProfileResolver` —
  the seam every Layer-B test relies on to drive Scarf against an
  isolated Hermes home. Bypasses cache + active_profile lookup; rejects
  relative paths. 5 unit tests + 3 ServerContext integration tests.
- `TestModeFlags.shared.isTestMode` — reads `--scarf-test-mode` once
  from `CommandLine.arguments`. Wiring only; gating sites (Sparkle,
  capability probe, first-run walkthrough) land as Layer-B exercises
  them.
- Layer A (`scarf/scarfTests/TemplateE2ETests.swift`): parses + plans
  the shipped HN bundle the way the app does at install time;
  asserts manifest, config schema, dashboard widgets, and cron prompt
  contract. Mirrors the existing site-status-checker coverage.
- Layer B scaffold (`scarf/scarfUITests/TemplateInstallUITests.swift`):
  proves the launch-arg + env-var plumbing reaches Scarf. Full install
  click-through deferred until fixture-Hermes-home and accessibility
  IDs land.

Wiki pages added separately on the `.wiki-worktree` branch:
- `Template-Ideas.md` — backlog of 9 v1-feasible templates +
  full-spec v3 epic for Project-Site-as-Living-Surface (eBay listings
  use case).
- `Test-Harness.md` — contributor guide for extending the harness.

Verification: scarfTests 124/124, ScarfCore 220/220, new Layer A 3/3,
Layer B scaffold 1/1, build-catalog.py + its 28 unit tests all green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/catalog.json

@@ -2,6 +2,76 @@
   "generated": true,
   "schemaVersion": 1,
   "templates": [
+    {
+      "author": {
+        "name": "Alan Wizemann",
+        "url": "https://github.com/awizemann"
+      },
+      "bundleSha256": "4889bc63c25e928ce96cf4032f248435348ee72d3b9c30ae5282361605a8616d",
+      "bundleSize": 8049,
+      "category": "news",
+      "config": {
+        "modelRecommendation": {
+          "preferred": "claude-haiku-4",
+          "rationale": "Simple HTTP fetch + filter + markdown render. Haiku is plenty fast and the cheapest option for a daily run."
+        },
+        "schema": [
+          {
+            "default": [],
+            "description": "Keywords or phrases to highlight in the digest (case-insensitive substring match against story titles). Leave empty to include every top story above the score threshold.",
+            "itemType": "string",
+            "key": "topics",
+            "label": "Highlight Topics (optional)",
+            "maxItems": 20,
+            "minItems": 0,
+            "required": false,
+            "type": "list"
+          },
+          {
+            "default": 100,
+            "description": "Only include stories at or above this point score. HN's front page averages ~150; lower this to widen the net, raise it to focus on viral-only items.",
+            "key": "min_score",
+            "label": "Minimum Score",
+            "max": 1000,
+            "min": 1,
+            "required": false,
+            "type": "number"
+          },
+          {
+            "default": 15,
+            "description": "Cap on how many stories appear in each digest. Avoids blowing up the dashboard list when HN has a busy day.",
+            "key": "max_items",
+            "label": "Maximum Items",
+            "max": 50,
+            "min": 5,
+            "required": false,
+            "type": "number"
+          }
+        ]
+      },
+      "contents": {
+        "agentsMd": true,
+        "config": 3,
+        "cron": 1,
+        "dashboard": true
+      },
+      "description": "A daily digest of HackerNews top stories. Pulls Hacker News' Firebase API, filters by minimum score and optional topics, prepends a markdown digest to digest.md, and keeps the dashboard's top stories list current. No API keys required.",
+      "detailSlug": "awizemann-hackernews-digest",
+      "id": "awizemann/hackernews-digest",
+      "installUrl": "https://raw.githubusercontent.com/awizemann/scarf/main/templates/awizemann/hackernews-digest/hackernews-digest.scarftemplate",
+      "minHermesVersion": "0.9.0",
+      "minScarfVersion": "2.3.0",
+      "name": "HackerNews Daily Digest",
+      "tags": [
+        "news",
+        "digest",
+        "hackernews",
+        "cron",
+        "starter",
+        "configurable"
+      ],
+      "version": "1.0.0"
+    },
     {
       "author": {
         "name": "Alan Wizemann",