feat(assets): probe-first resolver + SPOT for IMAGE_NAME/PORT + README screenshot

Probe-first asset resolution (regression fix)
---------------------------------------------

cache_manager.cache_file() returned either a relative cache path
(success) or None (failure). The previous app.py fallback
asset['cache'] = cached or asset['source'] mixed both types into
one field, which the template wrapped in url_for('static', ...)
regardless — producing broken
/static/https://file.infinito.nexus/.../logo.png URLs whenever the
source couldn't be downloaded.

- New app/utils/asset_resolver.py: HEAD-probes the URL (3 s
  timeout, image/* content type). On hit, embed directly via a
  new external_url field — no download required. On miss, fall
  back to cache_manager.cache_file. If that also fails, expose
  the source URL via external_url so the browser shows the alt
  text instead of an empty src.
- app.py exposes an asset_src(asset) context processor that
  picks external_url first, then url_for('static', cache),
  so the template never wraps an absolute URL in a static prefix.
- Templates (base, navigation, card) switch to asset_src(...) and
  gate the card image branch on cache or external_url.
- 16 unit tests cover every probe/cache/fallback branch; one live
  integration test exercises the canonical
  https://file.infinito.nexus/assets/img/logo.png to prove the
  probe-first path works end-to-end (cache dir stays empty).
- config.sample.yaml: new Infinito.Nexus card driven by the same
  canonical asset URL.

Single source of truth for IMAGE_NAME and PORT
----------------------------------------------

- env.example is now the only place the literal values live.
- Makefile and docker-compose.yml reference \$(IMAGE_NAME) /
  \${IMAGE_NAME:?…} (same for PORT); no defaults, no silent
  fallbacks.
- New make env / make config bootstrap .env / app/config.yaml
  from their checked-in templates. Idempotent.
- All container-using targets depend on the two bootstrap targets
  so a fresh checkout runs in a single invocation.
- Recipes source .env at recipe-execution time so they pick up a
  freshly bootstrapped .env in the same make invocation.

README
------

- Screenshot added under the title.

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

app/app.py

@@ -3,14 +3,16 @@ import os
 
 import requests
 import yaml
-from flask import Flask, current_app, render_template
+from flask import Flask, current_app, render_template, url_for
 from markupsafe import Markup
 
 try:
+    from app.utils.asset_resolver import asset_src, resolve_asset_cache
     from app.utils.cache_manager import CacheManager
     from app.utils.compute_card_classes import compute_card_classes
     from app.utils.configuration_resolver import ConfigurationResolver
 except ImportError:  # pragma: no cover - supports running from the app/ directory.
+    from utils.asset_resolver import asset_src, resolve_asset_cache
     from utils.cache_manager import CacheManager
     from utils.compute_card_classes import compute_card_classes
     from utils.configuration_resolver import ConfigurationResolver
@@ -43,24 +45,16 @@ def load_config(app):
 
 
 def cache_icons_and_logos(app):
-    """Cache all icons and logos to local files, with a source fallback."""
+    """Resolve every icon/logo/favicon to either a local cache path or
+    an external URL (see ``resolve_asset_cache``)."""
     for card in app.config["cards"]:
-        icon = card.get("icon", {})
-        if icon.get("source"):
-            cached = cache_manager.cache_file(icon["source"])
-            icon["cache"] = cached or icon["source"]
+        icon = card.get("icon")
+        if icon:
+            resolve_asset_cache(icon, cache_manager)
 
-    company_logo = app.config["company"]["logo"]
-    cached = cache_manager.cache_file(company_logo["source"])
-    company_logo["cache"] = cached or company_logo["source"]
-
-    favicon = app.config["platform"]["favicon"]
-    cached = cache_manager.cache_file(favicon["source"])
-    favicon["cache"] = cached or favicon["source"]
-
-    platform_logo = app.config["platform"]["logo"]
-    cached = cache_manager.cache_file(platform_logo["source"])
-    platform_logo["cache"] = cached or platform_logo["source"]
+    resolve_asset_cache(app.config["company"]["logo"], cache_manager)
+    resolve_asset_cache(app.config["platform"]["favicon"], cache_manager)
+    resolve_asset_cache(app.config["platform"]["logo"], cache_manager)
 
 
 # Initialize Flask app
@@ -83,7 +77,10 @@ def utility_processor():
         except OSError:
             return ""
 
-    return dict(include_svg=include_svg)
+    def template_asset_src(asset):
+        return asset_src(asset, lambda filename: url_for("static", filename=filename))
+
+    return dict(include_svg=include_svg, asset_src=template_asset_src)
 
 
 @app.before_request